A thread I started on the topic, a few years ago. Not just Montreal (as we were visiting both there, and Quebec City), but definitely some good suggestions.
We happened to arrive in Montreal on a Monday that was some kind of holiday, and it was a bit tough to find a place to have dinner. Might have been easier had we been in the city itself; we were in a suburb of sorts, Longueuil - convenient for us, as it was walking distance to a commuter hub including the subway.
The botanical garden was great, though we managed to find the longest possible route to get from point A to point B at any given time, and the paths were not well signed. I was proud of myself for being able to ask a staff member directions, in French.
In the touristy areas, you’ll find that most people speak a fair bit of English (though someone I asked, when we were using an ATM, did not). More rural areas, possibly not as much; we stopped in Trois Rivieres for dinner en route to Quebec City, and didn’t hear any English; ditto a couple years later when we took a VERY rural route back from QC and stopped in a tiny town for a snack.
We did a whale-watching tour, but we were in QC at the time, not Montreal; it was a 3 hour ride to get there, so it wouldn’t be terribly practical from Montreal, I imagine.