Will the natives of those islands be shipped off as slaves or wind up as dinner?
Hard to say, but it's not really like either fate has much to recommend it.
But what would these slaves be used for? As Jared correctly pointed out earlier, Aururian sugar would be significantly more expensive to ship to Europe than Caribbean one was, and kunduri plantations, most probably, wouldn't need as much labor as OTL Queensland's sugar-producing estates did.
Kunduri is going to be an interesting crop, although I suspect that most of coastal Queensland is too wet for it. Inland is really where it shines... that, or an otherwise drier climate.
Sugar, now, may or may not be cost-effective in Asia (see below). On reflection, though, there's one incontrovertible market for sugar: within the Third World itself. Sugar plantations in north-eastern Queensland would be excellent for growing enough of the crop to trade it to points further south and south-east: the eastern seaboard, Aotearoa, and even around into the southern coast. This could be both for useful commodities in themselves, but also for spices and kunduri which could be profitably exchanged somewhere in Asia.
Far north Queensland could, in short, become a very productive regional trading hub with sugar as its own commodity and shipping bringing in the rest.
Moreover, even what labor kunduri culture does need, would be provided mostly by Aururians themselves, as they have the know how, and there are a lot more of them than there are Pacific Islanders.
Pretty much true as far as kunduri goes, although forced labour is always useful in a time of labour shortages (ie Old World epidemics).
As far as sugar goes, well, growing it in plantations in OTL was a fate which pretty much any sane person would avoid if they had a choice. Parasites, disease and climate saw to that.
Far north Queensland would actually have fewer disease problems than the Caribbean - malaria is less of an issue since mosquitoes there don't transmit it as well, and yellow fever may well not get established at all. Still, it won't be a pleasant task for people to do willingly, and so it might be done unwillingly.
As for head-hunting-cum-Maori-colonization in Polynesia and Melanesia - well, there was an example of these things in OTL (I mean the Moriori's fate, of course), but the fact that this example of Maori's maritime conquests was the only one speaks for itself. There were reasons that discouraged Maori from going overseas, even when they had access to European firearms and ships.
As Admiral Matt pointed out, given the demographic hit from diseases and already low population, it's amazing that the Maori accomplished even one raid. Given what they're like ATL, I wouldn't put anything past them.
ITTL, Aotearoa is far more densely populated, so demographic pressure should be higher, but would it be enough to force one iwi or another to sail in search of greener pastures instead of just trying to kill a neighbouring iwi, as they mostly chose to do in OTL?
One possibility is that defeated iwi may, by negotiated settlement with the victors,
vacate their land in exchange for being allowed to sail off elsewhere in search of conquest. Perhaps.
Disagreement. The promising sugar land in Aururia is little more populated than in OTL. More to the point, absolute Aururian population numbers are beside the point. The continent's distance from Europe and Asia means that it will be exposed to a new epidemic or two every generation for more than a century. The result will be persistent population contraction, setting labor costs high - there will always be not quite enough people to do all the things that were planned a decade before.
Yup. This is going to be a huge - and persistent - problem. The short-term demographic effects aren't going to be as instantaneously severe as the multiple waves of die-offs which Euro contact brought to the Americas, but there's still going to be a long, severe decline which will see at least two-thirds of the population lost, if not more. And as you say, each decade or generation, things get worse.
Is there any reason sugar couldn't be sold to Japan, China, Indonesia, India, etc. instead? Did they already produce the stuff?
It could certainly be sold, if grown. Whether it's
profitable to sell it, given that there's existing production there, and the shipping distances, I'm not sure.
Misunderstanding. I do not see any "promising sugar land" in Aururia (that is, before steamboats would make shipping cheap enough - more on it below, in response to truth is life's question). I do see promising kunduri land in Aururia, though (similar to tobacco plantations of OTL Virginia), and kunduri-growing region (that is, Tjibarr) is fairly densely populated by 1618.
I see kunduri and sugar as complentary crops, not competing ones. The best zones where kunduri can be grown aren't really the same as those where sugar can be grown. Essentially, the wetter the better for sugar, while waterlogged soils are very bad for kunduri - the plants will probably rot.
Its population will decline after the contact, of course, but still, there will be hundreds of thousands Aururians left alive, with most of them being peasants, ready and able to grow kunduri. Of course, labour's cost will go up, and slave imports may go long way in lowering "wages" - but slaves themselves are not without cost. Our prospective kunduri estate owner would have to pay Maori (or European) slavers full price of catching/buying these Melanesians/Polynesians and transporting them to Aururian ports. It may be cheaper to control Aururian kunduri growers (through local aristocracy, if possible) than to ship new field hands from overseas.
For kunduri, I agree that it's most likely that mobilising locals - with perhaps varying degrees of force - makes more sense than importing slaves, save perhaps in a couple of areas in the north of the continent (ie where's not currently much in the way of local population.
Sugar is iffier...
I would think that if slavery would get introduced despite these hurdles, most slaves would be imported from Asia (especially Indonesia), and not Oceania, as it makes sense for European traders to buy slaves themselves, without Maori intermediaries, and there are much more people in Asia than in Oceania. The Dutch did it to some extent in OTL, with the end result being the Cape Malays (descendants of Malay slaves transported to Dutch African colony).
If a sugar slave economy does exist, there are multiple sources. I could see Maori POWs being shipped to northern Queensland, either by Maori or Europeans traders. I don't so much see Maori becoming intermediaries in trading Oceanian slaves to QLD, but then there's places close to Queensland where the Europeans (or, even, Aururians) themselves might go. (Melanesia, in particular). There are historical precedents for that, too.
Of course, I'm not yet sure that a full-blown chattel slavery market will exist. Some forms of more unwitting or unwilling labour may be more possible, though, as happened with the blackbirders in OTL.
To my best knowledge India was the first country to produce sugar, so yes, they did produce it (and transferred their skills to China and Indonesia) well before da Gama appeared in Malabar. Japan imported sugar from China, as the four main islands are mostly too cold to grow sugar ane (the Ryukyu chain is suitable for sugarcane, but it wasn't part of Japan before 1870s).
The thing is, economics was for Chinese sugar exports to Japan, but politics (well-founded anti-Japanese feelings in China) was against them. In OTL, economics won most of time (through bribes to Chinese officials, among other things). If ITTL Chinese government somehow does prevent the Chinese from trading with Japan (including trade through European intermediaries) - then Aururian sugar has some chances (but again, the Philippines and even Java are far closer to Japan than Aururia is, so even then, Aururian sugar is in worse position on the Japanese market).
The economics of *Queensland sugar is something I'm really not sure of. On the one hand, Queensland has a very good climate for it and will be relatively free of some of the problems which occur elsewhere (mostly disease). On the other hand, the shipping distances won't make things cheap, and there's not a native labour force in the immediate sugar regions, while there is in Asia. On the third hand, getting a native labour force may be relatively cheap if the Maori are selling off excess POWs or if *blackbirding is set up. On the fourth hand, either of those labour sources are more vulnerable to Old World epidemics of the sort which will be hitting with grim regularity.
In short, this is still something I need to think through.