The Battle of Passchendaele, also known as the Third Battle of Ypres or simply Third Ypres, was one of the major battles of World War I and occured in 1917. the generally accepted dates are 11 July 1917 – 10 November 1917.
At this point, the whole of the Canadian Forces on the western front were equipped with the ShtMLE MkIII and ShtMLE MkIII* (the rifles were not reneamed to No.1MkIII/MkIII* until 1928).
The shortcomings of the Ross rifle were made apparent during the Second Battle of Ypres in April 1915. The rifle showed poor tolerance of dirt when used in field conditions, particularly the screw threads operating the bolt lugs, jamming the weapon open or closed.
By the time of the Somme battles of July 1916, Sir Douglas Haig, the new Commander-in-Chief of the British Expeditionary Force, had ordered the replacement of all Ross rifles in the three Canadian Divisions by the Lee-Enfield, which was finally available in quantity.
So to make a long answer short, by 1917 there were virtually no Ross rifles at the front with the exception of a few rifles retained for special purposes like duty at the rear or for sharpshooting.