(Montreal is in Quebec, not France)
Yes, they can speak French although they need to speak English when someone needs to talk to them in English.
I've never been too comfortable with hearing other languages on ATC because if you only speak english you will only be able to understand transmissions meant for you. This might decrease your situational awareness to traffic in the area (knowing what's going on, etc). But I'm not a pilot so I don't know if this is true.