The problem for the Soviets would have been a lack of landing craft etc., and the lack of experiance in amphibious assaults. First, the Soviets have no Pacific Fleet worth mentioning to support a landing. This alone gives the Japanese an excellent chance of throwing any landing back into the sea. Japan is largely out of range of Soviet air power which only excerbates the problem.
While the Soviets might have landed on some of the smaller northern islands that were poorly defended they could not have managed a landing on anything with a substancial defense force on it. Even the poor Japanese coastal defenses could have made a hash of a Soviet landing.
For the Soviets amphibious assaults and operations requiring sea power were not in the cards for them.

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