Are dogs allowed on public transportation?

I live in Toronto, Ontario and here it's really common for dogs to go into public transit with their owners - of course these dogs needs to be held with a leash to ensure they don't just anyone, but it's allowed. I think here, it's more based on your dog - if your dog is good and behaves well with other people, then it's okay but if your dog starts causing problems, you'll probably get kicked off the bus. There aren't too many 'off-limits' places for dogs here but I know that some buildings don't allow you to have them but that's normal, I think.