So far, with a charged battery, I've had no problem starting the car down to -15 Celsius. It helps to pour boiling water on the injectors to help warm up the engine head. I don't have the option of plugging the block heater.
This morning it didn't even turn over, and the way the relay acted really leans me to think the battery was low. Might not have started with a full battery, but that's another story... :^)
P.s. I live in Montreal too. What type of car do you have? You can see mine at my web site below. We can wave if we see each other. :^)
1982 300D - <A HREF="http://members.xoom.com/nicodore/