I worked at Ontario Place last summer and saw the accessablility first hand. As I'm a student I can't afford a car and parking pass, so was forced to take the 511 streetcar to the ex, and walk from there. Almost late for work every day! I think they could run either the 511 or the 509 south so it ends up near the OP main entrance.
Ah yes, the summer job. For the summer of 1992 I worked as an Admissions person at OP, when we had to wear full woolen pants and blazers (now, IIRC, they were shorts, etc..). In the summer of 1993 I worked as a Parking Lot attendant at OP, which was much easier, as that summer was one of the rainiest on record, so I sat in my booth in an empty parking lot reading books and playing pylon hockey with the others.
As for getting there from my parents place at Warden and Kingston Rd., it was awful. I'd wait ages for the #12 Vic Park bus, and then ride the subway to Dufferin, where the slowest streetcars in existence would trundle down Dufferin at 20 kph (during track replacement, the substitute bus was a rocket by comparison) , from the CNE I'd then have to hike across to Ontario Place. It usually took at least 90 minutes to get to work. So, I gave up on the TTC, and began riding my bicycle instead, which would normally take about 40 minutes. I'd ride down Kingston Rd to Queen, and then down King to Bathurst, over the bridge and into OP. If I had an early morning weekend shift, I'd ride along Lakeshore, and if I had time to kill, I'd take the Martin Goodman trail along the Beach. It was rough on the the late night rides home, but my girlfriend (now wife) would meet me at her place in Beach(es) with a tall drink.
If you can swing it on your bike, I'd scrap the TTC ride altogether.