I lived in a PassivHouse in Germany. Didn't need to heat if it was more than 4C outside (less if more people were at home). I never experienced -40C, but at -20C it worked fine. Probably the only time all heating had to run to some degree 24/7. I'm sure that -40C would've been fine as well.
In the end it all doesn't matter. You build the house to some standard and then design the heating system to be able to cover thermal loss for the expected temperature range. In Canada you'd probably just add twice as much heating as you would in most of Europe. But especially at those temperatures, very well insulated homes will save a ton of money.
The only part that kind of worked less well at very low temperatures was the heat exchanger for the ventilation system. It didn't run at full capacity if it was well below freezing. But I guess there are other systems out there which are designed for -40C as well.
In the end it all doesn't matter. You build the house to some standard and then design the heating system to be able to cover thermal loss for the expected temperature range. In Canada you'd probably just add twice as much heating as you would in most of Europe. But especially at those temperatures, very well insulated homes will save a ton of money.
The only part that kind of worked less well at very low temperatures was the heat exchanger for the ventilation system. It didn't run at full capacity if it was well below freezing. But I guess there are other systems out there which are designed for -40C as well.