It is quite obvious that our politicians are bought out by the real estate industry. They lack the conviction to act for the people.
The "downside" you mentioned does not make sense. If the employment is temporary, the employees typically rent, not buy, houses.
Sure, we do not know whether foreigners are real causes of the bubble. Therefore, taxing them would not affect the housing market, correct? 
There is no harm to us Canadians either way for a foreign tax. ... wait, unless you work in the real estate industry.