We tied the defence of north, was told it was a narrow defeat then japan moved in.....

It would be a sweet combined arms map with armoured vehichles and light tanks, there were a few border skimishes and battles like the Battles of Khalkhyn Gol between Russia and Japan. 

Unfortunately i wouldn't know, i was hit by crazy lag spikes which made my life as a rifleman all that much harder and had to quit. :/

I was surprised this isn't a post at /r/paradoxplaza, where this would also be a bit weird(in the context of HoI).

So did the Germans get replaced by the japanese on the battlefield too?

So japan invaded russia and switched to the allies....