Telescope equipped Ross rifles were requested by the UKin 1940 after Dunkirk. Canadian reply was that all were needed for training. At least 80 Warner & Swasey scopes were taken to the UK by the 1st Cdn. Div. in 1940. These were fitted to P14 rifles in the UK by persons unknown. Ross MkIIIs with Warner & Swasey scopes were used for training in Canada until at least 1943, in 1944 it was recommended the scopes be scrapped; it seems most were. This is all from "Without Warning". Pacific Coast Militia Rangers were issued the MkIII in WWII as well as Winchester 94 and M17 rifles. Photos show Rosses being used by Veterans Guard or a few other security details in Canada I believe. I have seen textual references to PoW camp guards using them for example.
Since the P14 was already on issue it wouldn't have made sense to introduce another rifle into overseas service.