Re: Japan invasion of US
Early on, you concentrate on infrastructure (i.e. transport escorts and transports) for Atlantic.
If Japan drops to Alaska, they’re screwing with their early progress in Asia, so you react then.
Around R3, you can overbuild on infantry a bit and do as follows:
Post a few infantry in West Canada. Build infantry at East US. Build tanks at West US. Keep a couple extra infantry in East Canada.
Now the West Canada infantry stay where they are, say 2-3. Infantry at East US move to East Canada for Algeria drop. West US tanks move to East Canada for Algeria drop. If Japan drops to Alaska, West Canada infantry and West US tanks move to Alaska to reclaim, and use the extra East Canada infantry for the Algeria drop and/or to replace the West Canada infantry.
If Japan moves in in force, that’s great. They totally screwed their progress in Asia, and you can see the thing coming a mile away, so you can easily prepare for it.