Mr. Mason's article makes no sense, just seems to complain that "supply" isn't the problem, though none of his proposed solutions address his concerns.

Mr. Mason's article appears to blame foreigners and greedy developers.

First, Mr. Mason provides no support for the suggestion that foreigners are having a material impact on the market, just that "everyone knows".  Taking that at face value then, the solution is to ban foreigners from buying housing in the first place?  Don't like how that sounds though?  Not PC?  Own your policy.  If foreigners are the problem, banning them is the solution.  Don't blame foreigners on one hand, then imagine there's some convoluted solution that involves Canada being "open" to all newcomers, just not in the housing market.

Second, Mr. Mason  seems to blame greedy developers, though he doesn't say so in as many words.  Again, where's the proof that developers are padding their profit margins so much, it's distorting the market.