The standard Canadian sniper's rifle of World War One was the MkIII Ross fitted with a Warner & Swasey "musket sight" purchased from the United States. However, armorers in the field did create sniping rifles using other scopes - in particular the Winchester A5. The A5 was a popular commercial rifle scope at the time, and it found its way onto military rifles for many nations - I have seen examples on Lebel and SMLE rifles as well as of course American Springfields and this Ross.

The A5 was a 5x magnification scope with external adjustments. We don't know when this example was built into sniper configuration, but it's provenance is solid (this sort of thing would be relatively easy to counterfeit). Personally, I would much prefer a Winchester A5 over the Warner & Swasey pattern...