There is only one country with the ability to overfly Canadian ground where there is anything worth flying over and that is the USA.
Sorry old boy, I think that the Russians could get a Bear (Tu-95 / 142) over some points out west. It's not whether the area overflown has anything of practical value; it's all about sovereignty, pure and simple. If them durned rooskies, to quote a character from Dr Strangelove, managed to overfly some part of Canada with impunity, then the perception of that nefarious act is damaging, some would say highly damaging, to Canada's international reputation, especially with it's southern neighbour. Politics is all about perceptions and I believe that pollies, use perceptions to judge and evaluate other pollies.
In the past 30 years our combat aircraft have been deployed once in a strength of 24 aircraft to the Gulf flying mostly CAP.
36 F35 would provide one operational squadron and one training squadron and provide attrition aircraft. These would provide our expiditionary firstline deployable aircraft for NATO and UN missions.
24 F15 air superiourity fighters for NORAD commitment.
36 AH-1Z Viper marinized attack helicopters to provide support to deployed ground forces and escorts for the Chinooks.
36 AT6 or A29 depending upon whatvthe USAF eventually buys. These for COIN, escort and low intensity operations where the air space is owned.
What little $$$$ we provide to the military needs to be effective and appropriate for the task . As I said before the use of fast jets are not appropriate for all tasks.
It's not about what's happened in the past, although that informs force planning. It's about the credible potential threats that you face in the future. Canada is part of NATO so you face a credible Russian conflict and history has shown that any conflict with Russia is no walk over. Ask Napoleon and Hitler about their experiences, for example. And you would be facing Russia on two fronts, one in Europe and the second in the Pacific.
What if China decided to ally itself with Russia and join the war? That has possibilities because it has advantages to both nations strategically, forcing the US, NATO, FYES & allies to fight a world war on many fronts. You, and the rest of us, would have a significantly larger problem. WW2 was won by the allies because Hitler was the best allied general, the Soviets bled the Wehrmacht on the steppes of Russia, the Japanese over extended themselves, underestimated their enemies, especially the USA. The USA industrial capacity to quickly provide the weapons necessary for the allies to win the war was phenomenal. Today it is a different story and I don't believe that the US has that same capacity, unfortunately.