"Better" performance doesn't matter. The only mandatory role for them is NORAD. NATO is a red herring. If we went to WW 3 would we really strip our NORAD force of any fighters? No. Is there a scenario in WW 3 where the Russians 1) bomb North America with conventional weapons or 2) use a limited nuclear strike?  No to both so that means they'd use ICBMs which fighters are of no use against. 

So what are the fighters for? To show "sovereignty" (by having some Canadian planes rather than US planes guard North America (really the USA) and to give the air force something to do (what NORAD does for US fighters) . It's a domestic political issue not a defence issue. 

The answer is to buy the fewest of the cheapest plane- both sticker and operating cost- and assign all of them to NORAD. That is probably 48 F-18s.