How does a city which is located in a middle of a plate get an earth quake?

I'm not familiar with the tectonic setting of the Toronto area, but you don't necessarily need to be on a plate boundary to experience an earthquake. Plate boundaries experience the largest and most frequent earthquakes, but they may occur along faults anywhere on the earth's surface. Areas that have undergone structural deformation in the distant past would have developed faults that can later be reactivated, and if they fail would result in an earthquake.