I have been updating my knowledge of Canada's quite limited use of the .577/.450 Martini-Henry rifle.
Canada never really adopted the Martini-Henry (nor the Martini-Metford or Martini-Enfield, for that matter). The .577 Snider-Enfield rifle was retained as our primary military rifle action from 1866 through 1898 when the "Long" Lee-Enfield was adopted ... and it wasn't until well into the 20th Century that all units had their Sniders replaced.
However, Canada did acquire a total of 7,100 Martini-Henry rifles ... 2,100 Mark I rifles in 1874, and 5,000 Mark III rifles in 1885. Although they never became general standard issue, the 2,000+ "Other Ranks" of the Militia Garrison Artillery Batteries were armed with them at some point during the 1890's.
Here is a period photo of a Canadian Artilleryman (the "ball" ornament, in lieu of a "spike", on his foreign service helmet confirms his branch of service) taken at Quebec City in 1896. He carries a Martini-Henry rifle, and is wearing "Lewis Equipment" in heavy marching order. As a Gunner, his tunic would be dark blue, not red. Note that he is also a musician.
I am the fortunate owner of a very nice Mark III Canadian-purchase rifle, which is prominently stamped with the government ownership mark used back then ... the initials "D.C" (Dominion of Canada) enclosed in a diamond. I've posted this image before, but thought I'd do so again to finish off this post. (The background is an 1889 phoitograph of Riflemen of the Queen's Own Rifles of Canada.) Click on thumbnail to enlarge ...