How will making housing harder to buy for ordinary Canadians ease the housing crunch? 

If you have fewer people able to afford a house due to higher mortgage qualifications, there will be fewer units sold, therefore builders will stop building as demand dwindles.  Less supply ultimately equals higher prices, but only being paid by the few who meet the new threshold.  

And the newly disqualified would-be buyers don't evaporate.  They fulfill their housing needs by renting; exacerbating the rental shortage and driving rents higher.

The current rate of mortgage arrears in Canada is 0.28% - this is fixing a problem we don't have.  But if you want to further divide the country in housing-haves, and housing-havenots, this is the way to do it.

For Toronto and Vancouver, limit foreign buyers.  Make it easier to build more and more units.  Make it easier for qualified Canadians to own their own homes.  A couple thousand empty units begging for buyers will bring prices down.