What time of the year are you going? We really enjoyed Montreal in the summer. We enjoyed walking around near the old port and taking a river cruise. My husband enjoyed renting a Segway to ride around for a while in that area. We just took a short river cruise, but there is one between Montreal and Quebec City if you’d like to make a day of it.
We also took a day trip into a more rural area, Mont Tremblant. Driving was a little tricky. If your family has any awkward backseat driver dynamics, you might want to plan in advance for how to handle the stress of unfamiliar road signs. We only rented a car for the one day we drove out of town. Within Montreal we were fine getting around on foot, by subway, and the occasional taxi.
I know a little French, but agree that the custom seemed to be just say “Hello” and everyone talks to you in English. French came in handy for reading a few things, but wasn’t a necessity.
Especially in the summer, you may want to take a look at what festivals are going on in Montreal when/ if you visit. There seem to be almost constant week-long festivals of various stripes. While we were there they were transitioning from a comedy festival to French-language music (Francofolies). You may enjoy the visit more if the festival going on while you are there is a good fit for your interests.
My personal experience in visiting Quebec City and Montreal was very positive on the language score. One time when we stopped for lunch in the countryside and no one in the restuarant seemed to speak English. But they were very pleasant.
The only nasty bit was a guy I was chatting with quite pleasantly until I betrayed a relative ignorance of F1 racing, and mispronounced “Jacques Villeneuve” at which point he proceeded to rant on and on about stupid Americans.
Also if you’re driving you should know the word for bridge – “pont”.
As far as language goes, in Montreal and Quebec City you won’t have any problem. Montreal even has a signficant minority of people whose first language is English. I used to be among them.
Yes, whatever you do, don’t bother with a rented car in Montreal. Anything you’d care to get to is within metro distance and parking is legendarily difficult, especially downtown, and confusing.
You can get a special discount transit-and-museums pass, if you’ll be visiting a lot of museums.