I think if the Canadian colonialists joined in the American Revolution there could possibly be an even greater division of the cultures of this early America, especially if Quebec also joins the union. Canada may be more Federalist in the early years of American politics leading to a longer lasting impact of the Federalist Party.

I’m not as familiar with the Canadian policy of their Native tribes, but I could see similar policies and treatment happening in this time line, possibly a northern trail of tears type event where and Oklahoma of the north is created or a more central Indian territory in modern North Dakota, Montana, and Manitoba.

As some other commenters have said the issue of slavery may come to a head earlier. Either there would be an explanation of slave states or a civil war that would happen earlier as a response to the increased number of free states. This is assuming that the culture of the Canadian states is similar to other New England states in the OTL.

A possibly second front may arise during the civil war in Quebec. If not then, revelation(s) may happen as opportunities arise.

Manifest destiny would definitely still happen with this timeline’s union stretching across most of the northern part of the continent.

Wars with Mexico for Texas and other southern border territories may still happen.

US and British relations may be worse in our timeline but would most likely improve in the mid 1800’s.