The heat should now be on in your apartments to ensure that it is a minimum of 21 degrees Celsius (69.8 F) all the time! The landlord has this requirement from September 15th to June 1st.
If you find your apartment cold, you should pick yourself up a thermometer and for a few days write down the date, the time, and the temperature in your unit. Measure the temperature in the middle of the room. If the temperature in your unit is less than 21C, let your landlord know, in writing (keeping a copy for yourself), that they must address the issue immediately. If the landlord does not address the issue, you can contact the City of Toronto Property Standards office at 3-1-1.
Best of luck and happy heating!