The answer is simple
1) Start raising interest rates - slowly but with a message that more is to come.
2) Kill the Places to Grow Act.  Forcing high density on cities simply increases demand in the urban core and drives up prices.  The Places to Grow Act is doing to housing what the Green Energy Act did to electricity prices.
3) No new taxes.  There is absolutely no evidence at foreign investors are distorting Ontario's housing market.  An analysis of the Census data show population is growing fastest in the Toronto area, KWC and Guelph and Ottawa. 
4) No subsidies for new home buyers.  Housing prices are rising because of excess demand and lack of supply.  Providing subsidies for new buyers is absolutely the wrong thing to do. 
5)  Saying "we must do something" is absolutely the wrong thing to think.  Try "we will only do something if the consequence really address the issue without any negative unintended consequences.