Only 10 stadiums are needed to host the WC.
Canada could propose the following:
West
BC PLace - Vancouver
Commonwealth Stadium - Edmonton
Replacement with temporary seating -Calgary
Regina Stadium - Regina (temporary expansion required)
Investors Group Field - Winnipeg (temporary expansion required)
East
Frank Clair Stadium - Ottawa (temporary expansion required)
New Toronto Stadium - Toronto (downsized post games for Argos or kept for an NFL team)
Rogers Centre - Toronto
Olympic Stadium - Montreal
Hamilton's stadium is a hole idk if they would use it. Maybe a final stadium in Quebec/Halifax to get a CFL team
To be honest you don't even need EVERY stadium to be a 50 000 seater, even in Qatar's overbuilt stadium plans most stadiums are in the 40 000 seat range and only 2 are over 50 000 seats. Russia is the same thing, only 2 stadiums over 50 000 seats. You only really need the 50 000+ seat stadiums for the quarters, semis, and finals. The rest of the buildings could conceivably be built to hold 30 000 to 40 000 seats (with ability to downsize post event to 20 000 or so)
I don't know why you are looking at all these big stadiums then:
Toronto has a soccer specific stadium in BMO. It could be expanded/renovated to seat approx 30 000+ from current 20 000 capacity
Montreal has a soccer specific stadium in Saputo. It could be expanded/renovated to seat approx 30 000+ from current 20 000 capacity
The Whitecaps have proposed a new soccer specific stadium in Vancouver. It could be built to accommodate a temporary expansion to 30 000+ seats
That leaves another 9 - 11 locations to be selected for stadiums including 2 new 'marquee' stadiums for the quarters, semis, and finals. I imagine that the preferred locations for the two marquee stadiums would be Toronto, Montreal, Vancouver (this despite their already having the smaller venues noted above), with Toronto and Montreal likely to be the primary locations due to geographic proximity.
The remaining stadiums I imagine would be some combination of temporary, renovated, and/or new structures. Ottawa Fury and FC Edmonton would probably get stadiums that could be stripped down after the WC. Quebec would likely demand a stadium (perhaps combined with a new soccer or CFL franchise). Winnipeg may get a few games at IG field. I could see a stadium built in the Maritimes (again combined with a bid for a CFL franchise). The remaining locations would be some combination of four of Hamilton, Missisauga, Regina, Calgary, Kingston, Windsor, Kitchener, London, Niagara, new Pan am stadium at York U, and Victoria. All of which could be built to allow for ease of tear down to a capacity around 5-10 000 seats and then donated to the municipality and/or local University/College.
In this way you are only ever playing in one active CFL stadium (IG Field) the rest would be built as soccer specific stadiums or if planned to be used by a CFL team would be occupied by said franchise after the WC.