PCW is the best park around. It's got 12 rollercoasters including an awesome suspended coaster and an alright SLC. IMO the best ride there is the Woodie, the Mighty Canadian Minebuster. It's a nice single out and back with tunnels and a helix.
As far as other parks, there is Marineland which sucks execpt for the huge dragon coaster which they have. (Which is really good)
Ontario place is located in toronto, but it contains no rollercoasters. It has simulators, a log flume, and water slides.
The CNE (Canadian National Exhibition) is also located in toronto, which contains a vast midway of classic rides, shows, international showplace, freakshows etc. It contains two rollercoasters. Unfortunately, It is only open in August.