Europe is cheaper and more fun. America's one advantage: nature, is matched and at times exceeded by Canada. Flights to warm places like Miami and SD take just as long as Mexico or the Caribbean.
Other than NYC and Utah-area national parks, I can't think of unique reasons for Canadians to vacation in the US specifically.
Also the US speaks english which can be nice for an easy vacation. No need to learn phrases or customs before going somewhere.
Lots of amazing outdoor adventures to be had in the USA. Now days I don't know anyone that goes to the states.
The only European airport that does this is Dublin, last I checked.
I remember flying Alaska Airlines out of SFO and when I went to check-in at the International Terminal, the gate agent said "Canada isn't International" and looked at me like I was the dumbest human on the planet.
Either she was seeing Trump's future, or....
FWIW, you have not lived until you see a way overweight man wearing only a tiny bikini bathing suit :)