Quebec is similar to France and there are a lot of American and international flights into Montreal every day. ATC speaks very good English but often speaks French to francophone crews so it can hinder SA of some of the non French speakers.
In the VFR world, most local pilots speak/understand both English and French so you hear both on the en-route frequencies and i would guess over 90% understand the other language perfectly well.
However, there are a lot of Chinese (and other nationalities) students in Quebec whose English is OK but heavily accented. When i am flying VFR with bilingual locals, they really struggle to understand what the Chinese are saying (in English) although for anyone who has spent time in China, it is pretty clear.
To my mind, whether in IFR or VFR, an effort should be made to use one language (English) even between two people who share a common other language. We should be concerned with everyone's SA, not just our own.