Canadian battleships could reduce US reinforcement needs

Would the United States still send fast battleships to Britain if Canada operated Queen Elizabeth-class ships?

Probably, but in smaller numbers because the Canadian squadron would already relieve part of Britain's worldwide capital-ship burden.

The United States historically reinforced Britain because Royal Navy capital ships were spread across the Atlantic, Mediterranean, and Indian Ocean. Three or four Canadian Queen Elizabeths would add another full squadron to that shared pool. Some American ships might still deploy, but fewer would be necessary to cover the same risks. The larger Allied battle line could also concentrate more force against Bismarck or release British ships for distant stations.