Heat Pumps are not common in the cold climates and because of that many people fear them in those areas. I had a ground source heat pump ("geothermal system") in Iowa and it was absolutely great. A/C was almost free and heat was still cheaper than propane. But we had to call around a LOT to find HVAC companies willing to touch it.
So look for companies advertising "geothermal" systems and you might have more luck. Air source pumps for heating a house aren't good in cold climates.. I'd say north of about the latitude of Indianapolis in most of the country. But south of that they work okay.. and like here in Tucson they are common for smaller houses.
For a pool heater though, since it's used in the summer for additional heating, it will work fine in your climate. So don't believe otherwise. It in theory is more efficient than gas but has less capacity.
If the unit is old and R-22, it might be difficult to service. The replacement coolants then to need other pieces of the system swapped out, because the replacement gasses aren't identical for pressure needed. And the stuff is $$$$$$$. It's often not worth it. If it's newer then you shouldn't have a big issue finding a leak, getting it fixed and then refilling with more modern coolant.
However, even R-134 and newer coolants are getting banned in a few years. So my advice is to fix it sooner than later, honestly. My personal thought on the coolant stuff is that is a great way for planned obsolescence and that is why you never see the manufacturers fight back on every more difficult regulation. Many cooling units use flammable coolant now too which is disturbing to me.
