The Foreign Enlistment Act of 1937 made it illegal to do so and many Mackenzie-Papineau veterans were blacklisted from service in the Canadian military. This law, still on the books, should also be applicable to those Canadians who now serve in the genocidal IDF, but it’s very unlikely it will be applied.
TIL. Probably not right away, but I think Western support for Israel is in it's waning days.