*For now*, I too support the 'America develops like Canada' theory....
I subscribe to a Loyalist America still very roughly paralleling our timeline, with the Anglo-Americans moving west, fighting over sectional differences, and let's face it, becoming a great power of some sort on the world stage probably occuring anyways due to them already happening or having the building blocks for it to happen ready by the time of the Revolution.
No one has remembered the Proclamation Line of 1763, one of the stated reasons for colonists to rebel. If they lose, that line gets enforced, though perhaps not rigorously.
And many Americans forget how Canada's history is so different from USA's.
Far fewer wars with Natives.
More treaties with at least some effort for the crown the keep their word compared to the US virtually always breaking treaties.
Efforts to create economic dependence instead followed by cultural assimilation. But still a higher percent of your nation being First Nation that the US. I think it's something like 8% compared to the USA's 1%.
And overall, a democratic tradition less rightwing than the USA. (Eg universal healthcare.)
But probably not a world power. I haven't seen any reason the USA would become so if it did follow the Canadian model. Manifest Destiny is much less likely if you have the Queen and her ministers telling you NO! until, what, the mid 20th century?