You can manage in Montreal, living in one of the Jewish communities, without speaking french. You will pick up some french once you are there and it definitely shouldn’t be something to worry about with respect to moving there.
Rent is relatively cheap (compared to Brooklyn or Monsey). But to buy a house in the Yeshivish neighborhood is expensive (more expensive than Monsey but less than Flatbush).
When people say the Yeshivish community is small, that is only compared to the Greater NY area communities. It is as big or bigger than Detroit, Cleveland, Miami and others.
There are a lot small shuls but no real big shuls and everything within the Yeshivish community is in walking distance. Because Montreal has significant Chasidish, Lubavitch, Sephardi and MO communities as well there is plenty of Kosher food.
There are two Yeshivos that run from Nursey through High School and there is one Bais Medrash (that has fallen on hard times lately but was great when I went there). There is a large Bais Yakov and Seminary.