There are a couple of factors in getting people out to other peoples games.
Because Canada is large it does take quite a bit of Time, Effort and Cash to get anywhere else short of the local playerbase. When I attended the Keystone event it took 2 1/2 days of travel and ~$400ish in Gas, hotels, food. Thats quite a bit and we carpooled and went cheap as we could on things. Having an Ontario player come to Alberta would probably be pretty expensive too, and vise versa.
Comroderie: It's unfortunate but alot of players from other provinces or even inside provinces don't know the other players so they are hesitant to spend alot of time and effort to go to a far away Sim when local sims seem to satisfy them. This is pretty evident here locally where when I run local Milsims have ~70 regular players but when we arrange to go somewhere, even to Edmonton the number drops to ~10 or less. Occasionally we can prod people to go to a unique event (Such as a recent trip to Mission BC's Ferry) but thats because it was a new and unique experience for most of the players.
The closest I think we've ever come to national level was the old Westcan games where we had the majority of Western provinces come together for some pretty good games. Mostly because there were game administrators/organizers from each province/city arranging things. Which like you suggested would work.
But really if you build it players will come. If there was an event that had good planning and support i'd be sure to prod my playerbase to attend it and put in a good showing.