I've been told by certain Americans (specifically from warm places like California) that we Torontonians/Canadians love two things: Cottages and patios. The Black Bull is a perfect example of just how much we love patios.
The Black Bull is famous for having one of the largest patios in the city. As soon as fairly decent weather hits, the patio is filled and never subsides until it's too cold to sit outside.
If you find a seat here, you're probably lucky, because it's usually too packed for a random drop in. Also, because of that, I'd say that if you plan on coming here, come early, and bring 4 people, because there's nothing more annoying than seeing a table for 5 occupied by only 2.