Eh, I could see Stalin trying to take down Poland somewhere down the line; he never really got over their victory in the '20s, especially because he used to be blamed for it. But it would probably be in the mid- to late-40s. A Soviet invasion of Poland does have the potential to start a European war with the Soviets vs. Poland, Britain, France, and maybe a few other states. Maybe the Japanese would get involved against the Soviets?
As long as the Japanese don't attack Pearl Harbor or accidentally kill some US citizens or something, the US'll probably stay out of war.
But again, Europe (including Italy) vs. the USSR, I could see that. Though most Eastern, Southern, and Central European countries really wouldn't know what to do. You may actually see another Phoney War break out, with more Soviet aggression once they complete the (bloody) conquest of Poland and, eventually, the Baltics.