the soviet army by 1945 was an exhausted animal. massive losses of men and material plus weak supply lines. these would have been annihilated by the baltic and polish resistance, as these were the most effective resistance formations in the entire war. the truth is also that the red army had a polish division who was prepared to defect and figfht against the soviets. it would have been chaos plus the ussr would be locked into fighting the us, and usa was far better off technology than ussr. plus usa air force was much stronger. the ussr would have no answer to any bombing campaign, for example.
Poland