Hi Lucie. No, I don't think there is. There is a shuttle that takes you from the designated parking areas in Oakville. There is no parking at Glen Abbey itself. I went a few years ago and you basically park in farmer's field and the shuttle (yellow schoolbus) takes you to the course. It's no more than a 10 minute wait for a shuttle....even less.
Have a look at the RBC Canadian Open Website...I have the parking page marked for you. There is also a toll-free number located at the top left hand corner of the page so you can call to find out for sure.
Renting a car would be the easiest unless you have easy access to a GO Train Station on the Lakeshore line (Union Station is the hub) Oakville Transit has bus service from the train station to Glen Abbey
Good tip traveller_yyz....