So the OP is a little vague about this scenario, so I've got three of my own to look at.
Scenario 1. The US and USSR keep their current geography and go to war. In this case, I don't see all that much happening, perhaps fighting in Europe or Asia, but neither nation would likely ever be able to establish a beachhead of any significance, since the defending nation could always draw upon more of their forces to repel the enemy, while the attacker would be logistically constrained and never capable of matching(unless they built up forces in a neighboring country prior to the assault, though that is a bit of a stretch). This would be a draw in my book.
Scenario 2. By act of ROB(random omnipotent being) the US and USSR as they were in 1941 are magically given a land border. In this scenario, the US gets stomped, the disparity of forces is simply too great imo, the USSR would likely capture a loot of land before the Americans could build up much to stop them.
Historically the Soviets managed to rebuild practcally their entire army after Barbarossa, but that was after having several million men slog down, and wear out the Germans, the US would not have this cushion. Another factor is where the lands of the two countries come together at, if the USSR invades from the west coast, than the US actually has a good chance to build up before it's too late, from say the east coast?.. The we're screwed pure and simple.
Scenario 3. If by act of ROB, the US and USSR are given a land border and say a couple years to prepare before the war than you've basically got the eastern front 2.0. This would likely end in a draw like scenario 1, but with many, many, millions dead on both sides.
I think things would still work out better for the US than the Soviets though, on account of their much larger industrial base. A war like this would likely cause the US to produce rediculously large numbers of AFVs and planes, even compared to our timeline. These US tanks would also likely be much more formidable than the Sherman's of OTL, since they do not need to be ahipped to another continent. To me, this setup is a lot like the historical eastern front with a dramatically buffed Germany(the US), not constrained by lack of resources, like rare metals and oil, and what ever the US lacked they would have the luxury of importing thanks to the US navy.
I consider the historical Soviet production figures would be similar to this scenario since it was already balls to the wall for them, compared to the US who sat far away from any exitensial threats.
