I am curious as to why you say an air sourced heat pump is not a good choice for your climate.

If you will have net metering then are you able to sell any unused electricity back to the utility company? If you can then powering you electric boiler is not free. It is hard to estimate, but 5 - 6 kW of solar panels is about what you will need to power the house without the electric boiler.

If you post your propane and electric rate a calculation can be done to determine which will be more cost effective. If propane is cheaper, than you could also use it for cooking, drying clothes, and domestic hot water.

IMO electric is a no brainer it is cheap .

You'd need to do calcs with your actual local prices of electricity/propane, but I don't see why a heat pump wouldn't be good for your climate. Should be able to do hot water as well year-round. You have woodstove for extreme cold events so shouldn't need to be too worried. Only serious question is how much/how frequently you will be using grid electricity instead of solar and how expensive it is.

Would cost more up-front than straight electric but should be considerable savings on ongoing basis.

Sophie nailed it (as usual). Please, do your own research on the "ups and downs" of different heating systems...because all types have drawbacks depending on the geographical location.

You say "you will have concrete floors...", so you haven't put them in yet? Are you putting the radiant heat in those floors? We did that for our northern NY home and love it!