Japan doesn't really have anything to bring to the table though, they invested heavily in their Navy and Air Forces, their Army was pitiful in comparison. Light tanks were the bulk of their armoured force, their medium tanks were just scaled up light tanks, and the only truly decent tanks they made were reserved for a battle that never happened. Their AT department wasn't great either, AT Rifles and some AT Guns, but mostly Mines, mines were the bulk of their AT. So unless you plan to balance them out by giving them effective but mega-cheap mines on their basic infantry, I don't see how they can reasonably compete with even the T-34/76.
It's the same problem USF has, the way they fought isn't accurately portray-able in this game. Their strengths were in things the series doesn't focus on, air power (Like USF in CoH2) and naval power.
I do agree 100% with another German - Russian matchup though, and the British too.
You could give banzai charge ability and expandable troops. Remember the Koreans who were conscripted? Sounds like more conscripts in the game though.
Just imagine the voices though......
I predict they get the obersoldaten's voice actor.