While I was at the Killers show in January at the ACC I realized that I really don't like seeing 'stadium shows'. They're impersonal such that the music, performance, sound and ultimately my enjoyment becomes watered down. THEN I look down at my ticket stub and feel the pain I most closely associate with being stabbed. Seeing as how I've never actually been stabbed I have to approximate the feeling.
The Molson Ampitheatre is the only 'stadium' venue in Toronto that doesn't inspire those feelings. It is able to retain some semblance of intimacy without sacrificing sound. I've mostly had seats but I've heard lots of good things about hanging out in the lawn. As it is outdoors the weather can definitely play a factor so make sure to check that before any concert.
I don't know if this policy still exists but it used to be that you could get into Ontario Place free on the date of the concert, with a valid ticket.