A few observations.
First - assuming the OP here I agree with those on this thread who say Japan doesn't have the manpower for a full scale war with Russia. They
might however have the manpower for a limited attack with the goal of taking Vladivostok. This would mean curtailing some of their southern Pacific operations (i.e. Malaysia or Burma) so that they would have enough manpower for the push or even siphoning off troops from the Chinese theater. This would be a better choice in my opinion because these troops are veterans from several years of warfare and would have a lot more experience.
Second - Assuming an attack on Vladivostok this gives a breather to both Chian-Kai-Shek and Mao who can then marshal their forces for a counteroffensive. If the Burma campaign is cancelled so that a limited offensive to take Vladivostok is possible then the Burma Road stays open, and the West is able to keep pouring supplies into China rather than risking the dangerous air supply bridge over the Himalayas.
Third - This also has ramifications for the Soviet Union. Stalin's spies assured him that Japan was going to move against the United States and Britain. This allowed him to transfer several divisions from Siberia to the West to stop the German onslaught. Without those divisions you definitely will have a battle for Moscow come spring of '42. And it is likely but not certain that Leventry Beria dies during the winter of a "tragic" illness (i.e. lead poisoning).
Fourth-The IJN will in the event of the above be pressuring for a final knock-out blow of the U.S.N. hoping that a decisive battle will bring the U.S. to the negotiating table. In this scenario I could see them postponing their Coral Sea operation and instead going for an all or nothing knock-out blow on Midway. This time with six fleet carriers including
Shokaku and
Zaikuku. The Battle of Midway is a far bloodier affair. How this would end I leave to the naval strategists here.
Finally - Japan has shot its wad with the Russian attack. It is likely that Japan is defeated before the atomic bomb is completed. However the war in Europe will be longer owing to the fact that the Germans are able to penetrate even deeper into Russia and Stalin may not survive as leader if Moscow falls.