For what it's worth.....
Based on much of the research I've done for another similar inquiry, it definitely falls into the "Trade Gun" category; which can be a rather large & somewhat diverse group. Here's some useless/useful background info that I dug up after my previous research. All of this info pertains to guns available through the North West Company, so it may or may not be relevant to ID'ing your gun.
Look for a makers name, such as Wilson, Sunderland, Wheeler, Barnett, Hollis, Ketland and Parker Field & Son. The majority of these gunmakers are, of course, from London - many came in various barrel lengths and many can be identified by a “serpent” or “dragon” side plate and oversized trigger guard.
Makers initials are generally, but not always stamped under the barrel.
The North West Company guns were marked with a Sitting Fox inside of a circle on the butt stock, lock plate and on top of the barrel near the lock. After HBC and the North West Company merged in 1821 the Hudson's Bay Company used a stylized “Tombstone Fox” cartouche stamped in the lock and on the top flat of the barrel.
The majority of these guns were a .60 caliber smooth bore, and the flintlock ignition versions were manufactured right up until 1875.