It's a mighty big park, but for the best odds I would recommend Pinery Provincial Park. I have always been successful there. It's just a bit far for me. There is a very healthy population of them and if you are lucky, you will find a nest. I have some e-mails in to a few locals from out that way. If I hear a nest has been found I will let you know.
Also in Guelph, which might be to far for you, there a a place called Preservation Park. There is a family of recently fledged young flying around there.
Pm me if you need any other info
Meghan
