I can't answer that question directly, but I know several people who might know it. One thing: the Canadian market was quite small and in the days before Autopact, and when the British Commonwealth still was a valid trading block, we had fairly high tariffs on a lot of goods coming into the country, even from the US, and preferential tariffs on Commonwealth goods. That explains the Canadian institution of the 'branch plant' where it made sense to build Chevrolets and Fords and Plymouths here, but not the regular Pontiacs, Mercurys, and Dodges. So, we had P, M and D as C F and P bodied cars, with the P M and D styling cues and badges, and their own line names. Usually, this meant the shorter wheelbase cars. So, for example, the Pontiac Chieftain was never sold here with its eight--all Pontiacs until late in the 50s were Chev 6s. Another thing--we had the Ford Flathead V8 for one full year after it was phased out in the US (its a trivia trick question) Pontiacs, Mercurys, and Dodges were very popular here as the 'slightly upscale' in name if not reality brands, and sold for a hundred or so more than their down scale stable mates.
Mercury was VERY popular here--much more so than it ever was in the US, and since Ford had been in Canada from early on, there were a LOT of flathead V8s running around, all running the more or less same engines. So, I can imagine that it was a popular engine to hop up and lots of parts were made specifically for it.