The loose , belted frock coat or shirt was also a feature of frontier riflemen in the 13 Colonies, as were the leather leggings, moccasins. Precise details of all the costume is a popular topic among modern revivalists or "buckskinners" , and one has posted some period pictures and quoted period sources here. These show or mention trousers, but the recurring phrase " Indian fashion" is key- as opposed to the English fashion of buttoned frock coat, shoes or boots, waistcoat.

The Canadian addition might be the hood, which is also found on the capote. I don't know much about the history of the Canadian capote. It has now commonly been adopted by buckskinners for winter wear, made from a Hudson's Bay blanket. But it also seems to have gotten tied into Canadian identity by the 19th c. (perhaps there was a sign at the border with "Welcome To Canada. Here Is Your Capote") ...which I suspect means that there has long been a temptation to portray the earliest Quebecois as wearing them- so, unless you can see a period source for it I would not place too much trust in a modern picture. The Wikipedia page has an 18th c. German portrait (https://en.wikipedia.org/wiki/Capote_(garment)#/media/File:Ein_Canadischer_Bauer.jpg) of a Canadian farmer wearing a capote without the hood.

Some more hardy buckskinners have now taken to wearing a breechclout instead of breeches- like seen in your links. Men's 18th c. breeches are indeed complicated things to sew, and a breechclout would therefore seem to be a cheap alternative. There is also a period reference to this, James Smith, describing his "Black Boys" of 1763:"As we enlisted our men, we dressed them uniformly in the Indian manner, with breech-clouts, leggins, mockesons and green shrouds, which we wore in the same manner that the Indians do, and nearly as the Highlanders wear their plaids. In place of hats we wore red handkerchiefs, and painted our faces red and black, like Indian warriors.". Your linked photos show a pretty uniform adherence to not only breechclouts but red leggings, white coats. But from period descriptions, there does not seem to have been the same "Indian dress" for everyone- it really seems logical to assume that some men had breeches, some did not, some had colored trim on their shirts, some did not. That, like now, people did not dress identically.

Smith, J. (2018). An Account Of The Remarkable Occurrences In The Life And Travels Of Colonel James Smith: (late A Citizen Of Bourbon County, Kentucky) During His . . . In The Years 1755, ’56, ’57, ’58 & ’59. Franklin Classics.