1939? Indeed, lots of fun.
Poland shits itself, having millions of Soviet troops to its WEST. However, all those Soviet tanks and planes will stop running inside days as fuel ends. A good thing for the Red Army that it still has lots of horse drawn transport.
Also - several hundred thousand PEOPLES Polish Army troops came along too. I imagine that some will rebel and break through to the Fatherland or go over the Allies, but I'd guess that most will be disarmed and/or massacred.
The II Republic mobilizes and prepares to fight.
The western powers suddenly have a headache ...
1945?
The Allies lost almost all their combat troops, in the ETO only REMFs and the forces in Italy are left. And the flyboys - these will be relevant and become even more self important.
USSR is screwed if the USA decides to push it eastward - the USA can raise another army, the USSR - after years of human wave attacks - cannot. Britain, after needlessly bloating the Bomber Command and Navy, is left with a small army which it cannot expand either. Canada screams in anguish as its male population is decimated, with most of the 20-30 age cohort simply ... gone.