Pictures would REALLY help to identify something such as this.
Your gun is an old French Army piece, likely from before the middle of the 19th Century. They had several models, most of them with back-action lockwork. That usually identifies a gun that was made new as a percussion (cap and ball) gun.
If you run into one with a standard front-action lock, you will find that a lot of them were cap-and-ball conversions of much earlier flintlocks, notably the Models 1763 and 1777, huge numbers of which were made for the Napoleonic Wars.
Quite a number of French muskets came to North America during the American Civil War, as both sides needed something that would go 'bang!'. Right after the War, these non-standard guns were sold off in large numbers, very cheaply. More of the same were sold off, very cheaply, through a number of outlets. The Adolf Frank catalogue of 1911 shows several types being sold from Hamburg, all at very low prices. Bannerman's in New York had some of these as late as the 1950s, believe it or not!
A lot of these went to places where people didn't have a lot of money to buy a new gun. Muzzle-loading guns still were in use by old-timers when I lived on Fogo Island, NDB, Nfld in the middle 1970s. They were using mostly 10s and 8s and the odd 6-bore. A gun the size of yours would have been called a 'five-eighths gun' or a 'slack three-quarter'.
I have a three-quarter gun made in London with a half-stock from the factory, a proper fowler with a 46-inch barrel and a Government-style lock; it is obviously a 'prentice gun from the filing. It is an 11-bore. I also have a big three-quarter or a slack seven-eighths gun with a 56-inch barrel on a converted Third Model Brown Bess lock, stocked to the muzzle, something between a 10 and a 9-bore: rather impressive, to say the least.
You will find these on the East Coast sometimes with replaced stocks, often locally-made from Birch, which is awfully heavy but will do the trick. If it should be a full-military gun, it might be an idea to try to restore it. But if it has a Canadian-made stock, it obviously carries a lot of Canadian history with it. In a case such as this, I think I would leave it as it is because to restock it would take away from its Canadian past and would destroy a little more of OUR heritage.
These things are a BALL to shoot!
But do have fun.
