For locations within a 6 or 8 hour drive a car beats a plane most of the time. By the time you drive hours early to the airport, park, check in, fly, rent a car and drive to your destination, the flying is only a small percentage of the time involved.
Toronto to Ottawa or Montreal are right on the edge of being a wash between driving vs flying for me. Once you figure in extra time for security, parking or cab to YYZ, then travel at the other end (plus some buffer for all the above) you save maybe 30 minutes.
and parking at Toronto Int'l isn't cheap.