I think Toronto's CMA population officially surpassing 6 million as of this year may also do a lot to legitimize it as Canada's mega city. 6 million sounds friggin big, at least by New World standards. Obviously not of the scale of New York, Rio, or Mexico City, but it's definitely upper 2nd tier (again by New world standards)

Including the entire urban area (Toronto, Hamilton, Oshawa) it is over 7.1 million.
I wonder when the Golden Horseshoe will reach 10 million? The core area is currently at about 7.5 million (Oshawa, Toronto, Hamilton, Niagara), but I feel like the Greater Golden Horseshoe (probably what will eventually be called the Ontario Megaregion or Toronto Megaregion) is definitely over 9.3 million by now.