I’m going to say that I don’t really like that this strategy is as effective as it is. If Japan changed the J2 buy to 2CV+1TT even full Pacific naval buys by USA wouldn’t stop this half the time, although obviously that would weaken the ground attack.
My view is that the game is a little broken here.
UK helping defend USA should stop this strategy pretty dead with troops/planes dropped in Quebec but really, should they have to? The other possibility is UK/Anzac retake of the Philippines which would help USA income if they can hold it but distracting Japan from its objectives may be enough.