Certainly an interesting topic, I'll admit that I'm not an expert on the subject but it strikes me that the Japanese army was very ill equipped to fight a large land campaign verses the Soviet Union. If I'm not mistaken the Soviets would have enjoyed significant advantages in man power, tanks and artillery and would have fought over more or less open terrain in Mongolia where they would have been able to bring all the superior firepower to bear.
As it is the U.S. ground forces enjoyed many of the same advantages in the South Pacific but due to the terrain they were limited compared to the ETO.
