"GTA and Vancouver RE markets isn't in purchases made by PR, visa holders, numbered companies, international students and Canadian citizens with contacts outside of the country?"
How could we stop them buying RE? Isn't it illegal to do so. Don't they have the right to buy property? You are mentioning Canadian citizens with contacts outside of the country. How in the world you could prevent a citizen from purchasing a property whether that person has outside contact or not? The fact is any demand accruing legally is the demand for that commodity. If the supply does not meet that demand, prices will keep on rising. The question is how could government the bring back affordability?  15% tax wouldn't do much.