It's not politically feasible to say "Come to Canada because it's easier then going to the US". Let's remember that AC, WS and others are subject to rulings / laws etc from Transport Canada. If we let people in for transit reasons, then in the eyes of the US we're simply letting in the evil doers and all those other nasty Axis of Evil types. This will undoubtedly cause more trouble then it's worth.

Nonetheless, it remains a fact (for now ...) that it is indeed easier to transit via Canada then the US because we still allow carry-on luggage and stuff like that. (But no lethal bottles of water of course.)

AC will have to offer or at least convince the travelling public that it offers similar convenience with respect to connections from A to B via YYx as what one could find by transiting ORD, JFK, SFO etc.

This will not be easy though because there are in truth, more options via the US then via Canada for now. For example, LH flies F from JFK but does not from YYZ / YUL. SAA flies from IAH but does not fly from Canada. AC will need to start offering these kinds of connections and options in order to fully compete with the US hubs. One way they could do this is to co-operate / integrate more fully with the *A partners, but this carries its own challenges.