Anglo Quebec was certainly at some point British enough that "by Jove!" would have been a normal expression, no?
In the Franco-Belgian BD classic "Buck Danny", in one of the early episodes, the authors have Buck use a super-British expression (as they quickly get more familiar with America, they'll never repeat that mistake in the entire series), which is something that only struck me re-reading as an adult who's familiar with the Anglosphere. Not 100% sure from memory but I'm pretty sure it's actually "By Jove!". A Continental Francophone writer in the late 1940s could easily make that mistake (they're familiar with it from exposure to English, but can't know Yanks don't use it.)
An American would just absolutely not say something like that.
It's like if you had a novel set in 1700s Paris, and one of the characters when pissed off goes "Criss de tabarnak!"