There is an Osprey on the Canadians in WWI that covers the uniforms and equipment. As mentioned above, the first contingent had tunics with a standup collar and 7 buttons, and a closer fit than the 5-button, fall-down collar British tunic. They also had leather Oliver equipment in place of the British webgear. Boots with cardboard soles that disintegrated in the mud of Flanders. The disastrous Ross rifle, plus Colt 'potato digger' machine guns. However, the Canadians replaced as much of their Canadian equipment as quickly as possible, so by summer 1915, they pretty much looked exactly like their British counterparts. For my 28mm version of 2nd Ypres, I simply used British figures, and added the coloured epaulets (red for artillery, blue for infantry, green for rifles) to make them a bit distinct.
The differences like standup vs falldown collar are going to be pretty difficult to see at arms length on a 28mm figure. Unless you're a particularly ferocious rivet counter, I'd say probably more trouble than it's worth to use anything but British figures.