I think the urban-looking footprint of Montreal may be bigger, but I don't think its downtown is. What I mean by this is that the urban-looking areas of Montreal radiate out from the downtown a bit further than in Toronto's case. Some of this likely has to do with the fact that Montreal is on an island and has therefore been forced by georgraphy to be somewhat more dense. Moreover, it's also an older city and thereby has more pre-car neighbourhoods.
However, Montrealers don't really consider a lot of what we may consider as "downtown Montreal" as downtown. If you stand at Peel & Ste-Catherines and walk 1.5 km each direction, that's basically what is considered downtown (which elimiates many areas like Old Montreal, Westmount, Mont-Royal, Quartier Latin, etc.). Whereas in Toronto, most people would consider King & Bay, Yonge & Bloor, Queen & Spadina, Jarvis & Gerrard and Harbourfront as all being "downtown." Most Montrealers I know consider Toronto to have a "huge downtown" and don't quite understand all the business nodes we have (e.g., Mint, Bloor-Yorkville, Yonge & Eglinton, etc.).
Indeed, I think it is fair to say that the STM's metro is more about moving people around the urban part of the city, whereas the TTC's subway tends to be more of a feeder system for the near suburbs. Ideally our streetcar system could play the role of Montreal's metro, but operating in mixed traffic makes it hard to do so.