And boom, there’s the problem. I have a heat pump for some bedrooms on the second floor but only because I have furnaces heating the other side. I am impressed how the tech has improved though.
Many other units have auxillary resistive heating when the temperature are that low, which is obviously less efficient than the heat pump, but is still better than needing to maintain a fossil-fuel furnace.
Even in Canada, though, I'd look into whether heat pumps with resistive auxillary heat are economical. If it only ever goes below -20⁰F for, say, a week a year, you'd probably still come out on top. And you'd definitely come out on top environmentally if your electricity is mostly green.
The cheapest aux heat is to buy a bunch of space heaters.
Aux heat for heat pumps (not mini splits) usually starts at 5KW (4 space heaters) and is a dedicated circuit direct to the panel and sized correctly. It's also contained in a steel enclosure with strict rules about distances to flammable items.
And at this point in time, the best air-source heat pumps are good enough until -25C. Meaning that you get CoP more than 1 at this temperature. So this would work for most of the US just fine.
The most common heap pumps use bore holes straight down into the rock here in Sweden, but lateral installs are marginally better performance (sun reheats soil every summer) if you have a big garden.
Heap pumps dominate in Sweden so the installers have a lot of confidence and give good practical advise.