The problem is finding an .ics file that you can import or subscribe to that has only holidays for Ontario. Canadian holidays is easy to find but I've never seen one for Ontario only. You can add the holidays to Outlook manually, here is a list of statutory holidays for Ontario through to the end of 2014.
If you want a Canadian holiday .ics file you can subscribe to that gets updated constantly so you never have to worry about it again I can recommend this one.
I subscribed to that one over 10 years ago and have never had to worry about doing any updates myself. It gets updated on a constant basis by someone else.