As pointed out in the above post, it was common for artists to do rough sketches and then finish them in the studio with props so it is not certain if the guns they are depicted as carrying are really what they had. And it wouldn't surprise me if the same one gun was used as the prop for both pieces depicted in the engraving. But they do look like some English trade guns or trade fowlers of that period to me. Quebec fell to the English in 1759 so by 1780 English trade items would have dominated. Someone more familiar with Native dress might be able to tell us more about what tribe they might be from, but there could be many possibilities, including Mohawk and other Iroquois.
The guns sort of look like some of the early forerunners of what became the common Northwest gun by around 1790. There are a few examples of English trade guns out there from around the time of the Revolution, ca: 1770s-80s, that basically have the straight lines of the NW guns, some with serpent sideplates, etc., but have the fancier fowler style mounts - acorn finial guard and stepped finial brass buttplate, instead of the simple sheet brass nailed buttplate and sheet iron guard which became pretty ubiquitous on the common NW guns later on. An example in Neumanns "Weapons of the American Revolution" comes to mind, and I remember seeing one in Jim Dresslar's collection back when he had his museum in Nashville Indiana. I think there might be an example by Wilson in one of the "Accoutrements" books as well.
If you trust the paintings, you'll note the wood cut back at the muzzles - which also suggests the possibility of an English officer's fusil - which were typically cut back to allow a bayonet. In the 1770-80s there is a lot of commonality in the basic lines and mounts for better Native trade guns, common trade fowlers, and officer's guns - they were all being made by the same makers in many cases.
Guy