People think that's a killer argument against heat pumps when it absolutely isn't.

In that sort of climate you get a hybrid system or just leave your old furnace in as backup. You'll use the furnace for the couple of days/weeks when it is below -25c/-13f and use the heat pump for the 6 months around that time window and save huge amounts of energy because you only use the heat pump when it's most efficient. A hybrid system will improve efficiency because it combines the technologies at transition temps while just keeping the old furnace as backup is obviously much cheaper, since you can also get a smaller unit than you normally would because you don't have to worry about the coldest period.