Lots to think about here. Thinking about the Polar Express and the entire game itself, the phrase, “For everything gained, there’s something lost” comes to mind. If Japan is in W. Canada, it halts the US shuck, but if they’re in Asia, it forces Russia to spend more to defend against Japan. Every game I play as Japan, the thought always crosses my mind to send my 4 transports to Alaska/W. Canada, but I can’t ever come to terms with it because of all those units you take away from Asia. Even if the US was out of the picture in Europe because of having to deal with the polar express, I don’t see how Germany could overcome Russia and the UK by themselves anyway.
As far as simply bidding a Jap transport….that works well regardless of whether you go after the US or not. It’s a win-win for Japan. I just won an Axis game with that transport in SZ50 implementing a KRF. It’s key to grabbing income very early on–income that you wouldn’t normally get a hold of that soon. I was able to hold Africa for a while with Germany as well. I admit, I was pretty fortunate to do that without the German bid. Overall though, I definitely recommend bidding the Jap transport.