Well, if protecting our arctic sovereignty is the priority for the CF then one has to ask are modern (and expensive) fighters really the best way to spend our limited capital budget? If we were REALLY serious about arctic sovereignty we should probably be putting more money into long-range patrol aircraft, the AOPS, coast guard ice breakers, search and rescue assets, environmental and customs policing, satellite surveillance, RCMP and Ranger presence, etc at the expense of new fighters.
Of course we still need fighters to replace the CF-18's and we need modern (and expensive) ones to last us for many years of service. I just think that trying to tailor them to a (in my opinion) very minimal domestic air-to-air threat at the expense of effectiveness for overseas offensive capabilities is a poor argument. I think we need to be more honest about what we need our fighters (and our other military hardware) for so that we can get what we really need. When the Thomas Mulcairs of the world stand up and say "is the F-35 the best suited and most cost effective aircraft to defend Canadian airspace?" our leaders should have the guts to stand up and say "No, but it's the best suited and most cost effective aircraft to defend Canada's sovereignty by blowing the crap out of the bad guys around the world that are threatening our global interests".