Yes, this one looks easy. The population of the Canadian outposts is initially pretty small and the population of the region is largely native, or French, or British military outposts, with control JUST transferred from French rule a decade earlier (from French Governors to the new rulers of the land, the English). Very few permanent colonists of the type that would have supported the goals of the revolution in the first place lived there.
The revolution starts, and English loyalist refugees start trickling north into the cities north of the St. Lawrence, like Montreal and Quebec. So the main populations are either loyalist refugees or people who just didn't care to join the fight in the first place. No incentive to join the revolution there...
You have the (at the time) Revolutionary hero Benedict Arnold attacking north to take these cities and, having failed to bring supplies or manpower for a real fight, ended up pushed back to the south. No incentive to join the revolution there....
Later in the war, the Canadian posessions become a place for the loyalists escaping the conflict to go and wait out the war, the larger loyalist population reducing the area's desire to join the revolution even further.
Thus, Canada never joined the revolution because they weren't pushed to, like General Arnold's gambit would have done, and didn't really have their own reasons for it. After the Revolution, it was a place for the loyalists leaving the new United States to move to without having to go back to England, so even post-Revolution, it wouldn't have switched.
The history of that time period (Seven Year's War through the American Revolution) was amazing, what I read of it.
I have ancestors from that general area, but they were Chippewa and from the Canadian side of the Sault, so I don't have tales of ancestors fighting in those wars (the European part of my family not showing up until the 1850s at the earliest).