Tin Lids states that R.J. Stampings in Montreal produced 1.8 million shells for the U.S. Military and there are no particular markings to distinguish them from the bodies manufactured in the U.S.; so just to clear up your first remark - Canada did not manufacture our own M1s, we bought them from the U.S. Thanks to Roger Lucy, the author of Tin Lids, I started looking seriously at M1 Helmets over 20 years ago and have managed to collect a number of variations in both the helmet shells and liners.
While the Canadian military certainly began in 1960 reissuing the M1 Helmets purchased during the war, Canada must have been purchasing additional M1 helmets as during my 34 years in the military saw every imaginable configuration of SWW and post-war M1 helmet being used. While in the Infantry Reserves in 1979, one day in the field, we received a bag of new Type 1 helmet chinstraps to attach to our helmets. Out came the pocket knives and everyone in the section proceeded cut the old chinstraps from their fixed-bale helmets - I managed to save a handful of chinstraps that day. Even by 1999 I was still finding guys in my Reg Force unit who were using unaltered wartime M1s.
Here are a few helmet examples as I have received them.
This one has a 1976 dated Type I Ground Troops Liner.
This one has a St Clair liner.
This one has a Hawley Liner.