Belatedly, for music... you might want to look at Stompin' Tom Connors for the Anglo-Canadian side of things (though it might be out of time period, started making music in the 60s) or Paul Anka. For the Francos... well, there's a million different small folk music artists in French Canadian culture. I'm not an expert on it at all, particularly in that time period, but for a "name soup" check out https://www.thecanadianencyclopedia.ca/en/article/pop-music-in-quebec-and-french-canada-emc/
The cool thing about Montreal is that prior to the separatist thing in the 70s and 80s, the city was very heavily loyalist Anglophone and made an interesting mix of people. Many Anglos (regardless of actual ethnic origin) were very British-Canadian in orientation, (I remember my grandmother using all manner of British terms in her day to day conversation, loyalty to the Queen and Commonwealth etc...). Quebec's population in the 50s was 15% Anglophone, but it was much higher in Montreal itself, and Anglos controlled a lot of the business and politics of the city. Given the divergence in timeline between real life and Fallout, you guys might want to stick with it, go with what happened historically or diverge into a what if.
I might poke my head in here, being a native Montrealer and a big Fallout fan. This looks super interesting!