Okay then, how would US adjust to facing Britain and Japan in the Pacific?
I mean in military terms, engagements on land and at sea.
The Americans outclass everything the British have on the sea, the Illustrious class was not comparable to the Yorktown class nor the Lexington class in terms of size or aircraft assembly. Doesn't matter if they build faster and more Implacable classes, they are too late and not even a little bit comparable to the Essex-class.
Since the British would probably send their home fleet to the Pacific to help the Japanese the Americans can rest easy about the Atalantic and maybe transfer a big carrier to the Atlantic Mid1942 after Midway(or something similar). They can counter the much older British battleships left behind in the Atlantic, the 2 North Carolina class battleships and South Dakota classes would stay in the Atlantic, brand new and outclassing and outnumbering the 5 King George V ships. They would probably start building more new ones for the Atlantic as well, Iowa class.
The problem for the US is reach. They would have a hard time reaching towards British territory, especially in the Pacific. Japanese strategic conquest is in the way. UK and Japan Joined they would cause a lot more problems for the American in the early stages, especially if the British could make the Japanese loosen their doctrine and use their cariers more. Combined with British carriers their force is scary and better than the American fleet.
It also largely depends on the answer to my question, what about the dominion?