No, Ontario’s last coal generation plant closed down in 2014. The current carbon dioxide intensity of Ontario’s electricity is 40g/kWh. Coal plants are in the region of 700g/kWh.
Ontario’s grid is relatively clean, you can look at today’s numbers here.
An electric bus is far more efficient than a diesel bus and even in places like Alberta that have a lot of coal generation diesel is still more polluting than electricity.