Are we talkin about Alpha 3?
In Alpha 3 Sea Lion is almost a given as you have 97% success rates with, at most, a loss of 2 aircraft to the AA Guns. From there you have all those nice transports with which to use to threaten Russia’s northern flank which should give them pause about sending a massive contingent into the Balkans (down by Greece and Romania) despite the obvious financial benefits.
What to do about it really depends on what Japan’s doing. If they’re trying to race across the Russian tundra, then go all into the Atlantic and try to free England. If they are trying for a VC win themselves, then you have to stop them and cannot dedicate much to helping Russia - which is why you see Russia falling most of the time.
What I’ve been doing is moving Australian, Indian and British aircraft to Russia when this happens, trying to give them enough time to defend while I stop Japan from “winning”.