I lived in Montreal for 4 years in the early 2000s and although I had no trouble with day-to-day living, I felt that social life as an English speaker was limiting. I enjoyed the cultural and restaurant scenes (Mtl Jazz Festival, Just For Laughs), but meeting like-minded people was hard.
And although it's possible to get used to, there are tiny frictions everywhere -- e.g. signage is generally not bilingual (you learn how to guess from context and from the Latin roots of words). This is not a big deal in real life because there's usually small print in English available separately as printed materials. That said, most cities in Europe, South America and Asia (the ones I’ve visited) have far more bilingual public signage than Montreal.
Not everyone is bilingual (only downtown and certain suburbs like NDG/West Island) so exchanging little pleasantries becomes more difficult, and there's always a guessing game going on as to whether someone looks like Anglophone or Francophone, even just east of St Urbain in downtown MTL. STCUM announcements are French-only so if there's an emergency on the tracks or a train schedule change, you have to ask around to see if someone can translate.
The tech scene was very underdeveloped when I was there. Big events/conferences/exhibitions were always happening elsewhere, e.g. Toronto, even Vancouver, but no one was coming to Montreal -- the biggest conference I remember was the grassroots Perl's YAPC. (although PyCon would eventually come to be hosted there in 2014-2015). Things are different now with the existence of many more startups, but the ecosystem is still much smaller than in many cities in English Canada.
You also have to understand that English-language culture in Montreal is an afterthought due the English-language market being smaller -- most big international productions (say musicals/concerts/talks... in fact, almost anything) will often skip over Montreal but will have a show in Toronto, and even smaller cities like Ottawa. I felt I was constantly missing out on stuff that was happening in the U.S. and ROC (rest of Canada).
I could've tried to learn more French, and though it would have eased things significantly, I suspect I would still have not been able to sufficiently integrate into society -- there truly are two solitudes (as Hugh Maclennan once put it) in Quebec society.
There's also a certain feeling you get in Montreal: it's a little bohemian (so a little gritty in parts) and eschews change (lacks a forward momentum and go-getter spirit in terms of embracing new things -- infrastructure is not as well kept up as in other Canadian cities, heritage building laws are very strict which is good, but it also means new developments are very restricted). I went back to visit a little more than a year ago, and nothing has changed.
I don't mean dissuade anyone from considering Montreal -- everybody wants different things in life -- but just wanted to provide a data point from someone who tried to live there unhappily. YMMV.