The backstrap markings are typical format for regimental markings. Striking through with a line was the way an armorer would cancel a previous mark when applying the new unit's initials. Regimental markings are notoriously hard to figure out at times because they changed over the years, regiments changed names or were amalgamated with other units and just to add to the confusion the unit armorer didn't always use the "official" unit designation. A very quick scan through Skennerton's The Broad Arrow the only CAM I could find was for the British Cameron Highlanders, but I believe the Canadians also had a Cameron Highlanders unit. OTC in a stamp often means Officer Training Corp, sort of the equivalent to a college ROTC. The EOTC could be something like Edmonton College OTC, just a swag on my part, But use by the Camerons during the war then transferred to a OTC post war would be a probable line of progression for a revolver, especially since post war they would have tried to standardize on the government issue sidearm rather than an outsourced piece.