Car rental SEATAC next summer. Pick up and drop off at the same place. We planed to see parks Banff and Jasper in Canada but they are in Alberta no more in BC. Is it allowed? Will we have to pay additional insurance or fees to drive to Canada?

Large rental companies ( Avis, Budget, etc) include insurance to Canada in your regular fees, but smaller or local companies don't. So just check with your rental company prior. I was there in Nov got a rental to cross into BC. Another tip: check with your visa or Mastercard, you can waive some insurance charges because you are covered (up to certain liability), but need to print out a certificate (call your credit card company and ask if you have this perk, then ask your car rental company if they take it).

No fees or extra insurance to Canada, at least driving to Vancouver was fine if you have unlimited miles. We drove a rental from Kalispell to Banff a long time ago, I don't remember the company or what charges were.

Check with your insurance company