When I divide the pop. growth in the Lower Mainland by housing completions, I get a number that is substantially lower than the average household size (~2.1 against ~2.6). Perhaps it's worth checking this for the GTA as well? For the Lower Mainland, this data suggests that ample supply is being made. The need then is to examine whether the supply being built meets shelter demand (would require legislation/ incentives to drive building of units with more bedrooms), as well as to assess whether this "demand" is being driven by demand for something other than demand for shelter (which has a lot less to do with population growth than it does with speculation [either foreign or domestic]).

It's worth noting that the population growth rate in the Lower Mainland was larger 10-20 years ago, when prices were relatively flat. And that rents here, even with recent increases, are less than the carrying costs for owning (very true for detached houses). This does not suggest demand for shelter.