I swore Hitler was a proponent of automobiles rather than trains, as the one true way to be able to 'see the country'. Trains would be used for goods and such, but the primary transport he envisioned was automobiles, the People's Car that would be eventually be known to the west as the...
Goering, looking upon these plans: those are great, but, where are the people going to sit?
There was silence for a moment.
"Herr Reischsmarshal, they're right there...- he say, timidly pointing at one o the many rail cars.
"You must be mistaken. Those are my bacon cars."
Pretty much this. While Prussia was undoubtedly the least of the Great Powers on paper, its ability to punch above its weight(on land) would make them an excellent choice to make sure France stays out of the lowlands.
Prussia's religious tolerance will help, honestly, and its military will certainly fare better than the Dutch one in the Lowlands. So long as the UK approves of it remaining under Prussian tutelage, I can see it staying there.
You'll need a PoD before Yalta. Best bet is for Germany to more-or-less stage a fighting retreat in the West, forgetting about driving them back to the sea and simply focusing on stalling for time while whatever units are not considered absolutely vital for that shipped to the eastern front, and...
Really, had he not defected, his face would be on the dollar bill, and we'd have a Benedict Arnold Memorial. I'm obviously using a bit of a butterfly net here, but you know what I mean.