Just spotted this on FB. Apparently Canada still harboured rascism back then. Still does, but thankfully much diminished.
https://www.canadashistory.ca/explore/politics-law/the-prince-the-pistols

The first of its kind!

Well, we aren't exactly inundated with posts about Texas here.   

Specific serial number records for Canadian military longarms are extremely sparse, and I am unaware of any for the Spencers.

Another interesting tidbit from Edgecombe: although 100 Spencer carbines were shipped to Fort Garry, only 93 were received ... seven of them apparently having been stolen en route!

He also references a record that, as of 1 April 1874, Fort Garry Stores still held all 250 Peabody rifles, but only one Spencer carbine.

Wow! Thanks so much for the background, and the photos. I got a real shiver from the pics.
As to your one point ... "In October of 1870, 100 Spencer carbines (along with 250 Peabody rifles) were shipped by the Dominion Militia Department to the Fort Garry Stores for service in "the North West Territories" (i.e what became Manitoba, Saskatchewan and Alberta.) Apparently, it was from these Stores that Spencer carbines were issued to the thirty Métis men hired as armed escort and scouts for the British contingent of the Boundary Commission surveying and marking the 49th Parallel west to the Continental Divide in 1872 and 1873.  These men were permitted to retain their carbines following their service."

Are you aware whether the serial numbers from the carbines shipped for service in the "North West Territories" were ever recorded?