Start looking at rentals now. Get an idea of what is available and the costs.
You can probably find someone willing to give you a smaller rental. Just keep in mind, that is illegal. Meaning, if there are problems with the rental and you complain, the landlord will just evict you. And you will have to live in worry everyday that someone will call to complain to the city. The landlord can get into a lot of trouble renting too small apartments for a family. Not really the type of person I would do business with.
You might begin to see why Canadians have only a few kids. Kids are expensive!
http://www.rentfaster.ca/listingsearch.php?sortby=price&quadrant%5B0%5D=NW&quadrant%5B1%5D=NE&quadrant%5B2%5D=SW&quadrant%5B3%5D=SE&beds%5B0%5D=4&beds%5B1%5D=5&beds%5B2%5D=6&beds%5B3%5D=7
(If this shows up with super expensive houses first, re-arrange the prices low-to-high.)
There`s a few townhouses in the NE for rent 4 bedrooms or more. About $1500 per month. That is very good for 4 bedrooms. Vista Heights is a nice area.