Before I forget, I noticed someone else was asking about driving in Canada and here is a link to all the provinces:
http://canadaonline.about.com/od/driverslicence/Drivers_Licences_in_Canada.htm
and specifically, Ontario:
http://www.drivetest.ca/en/license/OutOfCountryDrivers.aspx
^direct link to information on exchanging an out of country license
As I understand it there are several pieces of documentation you can provide, I have resided in Canada since July 2010, so my 6 months are up and my US license is about to expire as I'm turning 21 in May. I believe you are eligible for a license if you can prove you are here legally for more than 6 months. :]