The Canadian infantry that went to Europe in the early years of World Wa rOne were equipped primarily with the Ross MkIII rifle. The Ross would become quite the scandal, and was replaced in service with the SMLE in 1916 – but as a sniper rifle the Ross excelled. Its problems in service were largely based on poor quality ammunition, and this was not an issue for the sniper corps. In addition, Great Britain was having enough trouble equipping its own snipers to have any extra scoped rifles to hand over to the dominions.
And so, the Canadians modified 500 Ross rifles into a sniper configuration using American-sourced Warner & Swasey M1913 “Musket Sight” scopes. These were 5x magnification prismatic scopes, also used by American forces on the M1903 sniper rifle and the M1909 Benet-Mercie machine guns. The scope was not very good, suffering from fogging and other issues, but it was available. The Canadian rifles were made in two batches of 250 each, one in 1915 and one in 1917. This was actually more rifles than needed, and many of them (including the two in this video) remained in Canada for training (and were used at least until 1942).
Canadian Warner & Swasey scopes can be identified by three elements. They have elevation dials marked out to 2400 yards, serial numbers between 1 and 500, and no data plate on top. Canadian scope cases are marked with the serial numbers of the scope and the rifle they were issued with.