There is a two volume set of books on Canadian Gunsmiths of the muzzleloading era, and it is true that Canada had a prolific gunmaking trade from coast to coast in this era right up to about the 20th century. When I was a kid in college, I happened to be in the University of Western Ontario, and in one of the halls there was a display of rifles from the shop of RW Soper of Canada West. It was a stand of about eight rifles, all half stocked, with walnut stocks and percussion locks, chequered wrists and in short, high end rifles. They resembled many of the rifles I've seen from the East Coast of the USA, but I didn't know enough at the time to examine them in detail. Too soon old and too late smart.
Whether or not your rifle is of Canadian manufacture, I cannot guess. During the period in which your rifle was in use, there was active movement across the 49th in both directions...could easily be canuck or 'mercan.