First, set up a US fleet to kill the German Baltic then Mediterranean fleets. Get 6 transports; three to move troops from E. Canada to UK (you march infantry from E. US to E. Canada), and three more to move troops from UK to wherever (Norway, Karelia, Archangel).
On the way, you will probably drop some guys in Africa.
Then you take the remnants of the US fleet and go hunt Japan.
What happens if you just try to build against Japan? Germany gets Africa and uses those IPCs to beat the crap out of USSR. UK without Africa can’t produce a lot. UK cannot reclaim Africa because Germany can smash the UK fleet with the German Med fleet and fighters and bomber. Germany is rich, UK and USSR are poor, Japan still runs cheapo infantry into the mainland, but switches to fighters and infantry instead of infantry and tanks. It takes a long time for a US Pac fleet to get going; two battleships, two carriers, a destroyer, four transports, five fighters, and a bomber are no joke to face down, and that’s what US is up against.
Late game, Japan is an easier target than Germany, because Germany can defend its capital with mass infantry, but also use those massed infantry to attack. But Japan can’t attack anyone unless it has navy and/or air. Once US has control of the islands and Asia, Japan can build 8 IPC worth a turn, hopeless.