Well, it depends what you want to do. Montreal is my favourite city in the world hands down, but Quebec city has amazing history and Vieux Quebec is quite lovely. Toronto is boring and ugly & much farther away. There’s so much to do in Montreal & is quite bilingual which is helpful.

Ottawa!
Ok, I know its not one of yoour options, but its only two hours from Montreal, and there is so much to see! I think I’d go with Montreal or Toronto, choosing from your list. CN tower is in Toronto, and the shopping is good in both.
Montreal would allow for a day trip (or overnight) to Ottawa. Toronto would allow for a hike down to Stratford to catch a play at the festival, depending on when you are going.

Montreal.

It’s a great city that I love with wonderful neighbourhoods and tons of things to do with music, food, people nature, etc.

I always enjoy myself in Montreal and it’s a very self-confident and vibrant city that loves life and people.

Er… Vancouver! Sorry, that probably wasn’t helpful.
I’d go with Montreal, but that’s me…