Thanks.
I only tried Royal Air Maroc for my first flight.
It was a one-way flight from Tunis to Montreal. I booked very late as I had to wait for my permit and flying to Montreal via Casablanca was much cheaper than the other options in that time, but henceforth, all of my flights should be Toronto-Tunis-Toronto. So I technically haven't tried any airlines yet and therefore have no idea which one should I choose. I think Air France has more flights to Montreal. So I am considering Air Canada, Alitalia, Lufthansa, Turkish Airlines and British Airways.