Admiral Halsey
Banned
Yes, American dreadnaughts were excellent. But at this point in time, the RN still has more. Plus, in this scenario, the RN is backed by the German Navy and the Japanese. That is already the top 2 navies in the world plus another in the top 5 (give or take).
I don't think the floor would be wiped with the USN. I think it would do a lot of damage to the joint Anglo-German fleet, but in the end I think it would lose.
Remember British and German shipyards were more geared towards mass building of dreadnaughts. This isn't WWII when the US had developed all the improved production techniques, etc. If the war lasted 10 years, sure the US could out build Britain and Germany, but not in the short term.
And see above, I do not think the US would want Canada to join. A vote would be decidedly against annexation by the US, so I think Canada would be given its independence.
And given the original timeline for the scenario which was 6 years(?) then it's entirely possible for them to have significantly increased the navy in size especially if until it was built up they used it as a "fleet-in-being"