The only site in the City of Vancouver that I can think of that could accommodate anywhere near 4M sq ft is the development rights Port Metro Vancouver has at Central Waterfront, but that is only about 2.5M sq ft.
Kerfoot's development rights over the CP tracks aren't even 1M sq ft, IIRC.
There is not even a full city block downtown that would allow anything anywhere near that large, as you'd be up over a 30 FSR.
There are several sites where 1M sq ft would be realistic though...