TIP: This is an ASTC member, so if you have a membership at your local ASTC museum, you can get into OSC for free. This is perfect for a good half day excursion.
Pros:
-Has some exhibits from when I visited as a kid 30 years ago. I can relive part of my childhood.
-Many interactive exhibits that are appropriate for kids of different ages. Kids love and want interactivity and the interactive exhibits are far better than the "watch this short film" exhibits.
Cons:
-Has some exhibits from when I visited as a kid 30 years ago. Get more new stuff in there.
-Not in the same class as museums in NYC and Chicago (Museum of Science & Industry, which is the largest science museum in the western hemisphere), but Toronto is quite a bit smaller than those cities.