According to this very important report (pdf):
Deadline 2020 presents the first significant pathway for relating the ambition of the Paris Agreement to action on the ground.
This would allow C40 cities, representing 650 million people and 25% of the world’s GDP, to deliver individual emissions trajectories consistent with limiting global temperature rise to 1.5 degrees.
The report lists the climate risks for cities. Extreme winters are the main risk for Toronto:
While the overall climate is warming the potential for extreme winter conditions is also increasing in frequency. Extreme winter conditions can increase demand on the energy sector resulting in brownouts and blackouts. Various health effects arise from periods of cold weather exposure, including frostnip, frostbite and hypothermia, with vulnerable populations particularly at risk. Extreme weather also puts stress on public infrastructure including roads and other transportation services