Well, they were weak, we were strong. They got most of their munitions, weapons, supplies, and food from us. We had the atom bomb, they didn't. Would have been interesting, to say the least.
Except when Patton wanted to keep going we didn't quite have the bomb yet. 9 out of 10 German soldiers killed in the war were killed by Russians. We could have done it, but not that easily (as Hitler found out).
Manhattan project started in 1939. Trinity test went on 7/16/45 and Hiroshima & Nagasaki were the next month. Granted, we used up the only two abombs that we had on the shelves, but you don't think we could have made more to bomb Russia with?