Canadian snipers were not issued special ammo because none was made.
They did, however, pick from what lots were available and run their own tests. When they found a lot number that shot especially well, a good supply was sequestered from that manufacturing lot and put aside for the Sniper section.
Following basic selection, individuals would conduct their own private tests for bullet runout, concentricity, seating depth, primer crimp and anything else which could be thought up, short of firing the stuff off. This was the same procedure as used in the Imperial Matches prior to the War.
Then followed zeroing of the rifles themselves, using the new Lot number of ammunition.
Generally, a rifle/ammunition combination would be deemed "acceptable" to Canadian snipers if it would keep them ALL under an English penny at 100 yards. Being that the Penny in use was about 1.2 inches in diameter, this standard would give acceptable performance out to 500. Some rifles, of course, would shoot better, but all rifles were checked out very carefully by the men who carried and used them.
Source of most of this information was Capt. D.C.M. Elliott, a Canadian who operated a Sniper group of 47 men which worked with the Lovat Scouts in the D-Day invasion.