Even better, once your fleet stages to 92, if the US is at war, they have no choice but to prepare to be attacked. That isn’t necessarily a good direction to go for the Axis (bc they can kill your fleet pretty easily if you invade from that direction), but it forces the US to place at least something there to stop you, and this is especially good if they did the heavy Pacific buys on US 1 and 2 because they may have as little as one combat ship, one transport, and a few men defending Washington. They are hiding behind that peace–however the only way you could actually deceive them might be if Germany was not at war on G3, but Japan then declared war on J3. Nonetheless, any competent player would still recognize the threat of being at war in the atlantic though the US is often not prepared for the Atlantic side of the war to begin.
Like the Sealowe thing, its better to threaten it then it is to actually try and execute this plan because the Allies still have to prepare for anything that you could potentially do, whether you have the odds to do it or not.
As a side note, I think it is really interesting that at the early war conferences, the US agreed with UK USSR that the Germans were the greater threat, and all agreed in principle that they would focus the majority of their economic power against the European Axis first. But, post war analysis has shown that (probably because of the difficulty of attacking occupied Europe without overwhelming force, but also possibly tending to kill the weaker dragon first/getting revenge) the large majority of the US effort up until Normandy was actually directed at Japan.