Will there always be a Canada?

No, but don't panic.  Geography, "Juice" and genetics are the big three factors with a wild card added.

Geography is the big building block. (1) The Saint Lawrence and Great Lakes will anchor the east for the foreseeable future.  The prairies ( the Canadian version of fly-over country) have a more natural north-south axis which is reflected in their settlement history. (Canadians were settling the American west, rather than the other way around at first.) The West Coast, despite the golden spike, the CPR and the CNR, is still more naturally a neighbour to Seattle, and the coastal area towards California.  As long as America (with the same zones and the Mississippi-to-the-Gulf drainage) holds itself together and as long as America is the greater and Canada the lesser, Canada too will hold together.  America is a teentsy bit less glued of late.

"Juice" is economic clout.  Oil and gas sometimes give an edge to the western prairies, and industry generally favours the Montreal-Toronto axis.    Our neighbours to the south have similar but bigger economies.  Game changers are coming.  The internet is making knowhow cheaply available everywhere.  Breakthroughs in energy like cold fusion will make power cheaply available everywhere too.  ["NASA's cold fusion tech could put a nuclear reactor in every house, car and plane"]Tuktoyaktuk will have almost the same resources at almost the same prices as Calgary.    A third factor is a glimmer but will be the norm soon:  Downloading and printing three D objects of great complexity, from car keys to special widgets to custom-fit clothing.   It seems silly to be concerned today but it leapfrogs over all the constraints of geography and changes the ground rules.  Transportation by ocean and river,  road and rail, and detours around mountains,  have defined the location and shape of countries and cities until today.

Genetics is the tribal stuff and Canada is oddly secure here, being such a mixup already.   We have little communal rage between tribal groups as is common in other lands where they killed and robbed each other. The absence of blood debts makes Canada easier to govern.

Wild cards happen such as a brilliant leader who may change our position in the world,  a new set of rules that could make Canada a lighthouse in a world locked down under the curse of crony-run socialism, a large meteor might strike near Peterborough,  glaciation may abruptly resume,  a tool may be developed to terra-form covered communities in the boreal forests, or we come up with a monopoly on some technological breakthrough.   "Only in Canada, eh? Pity! " would refer to something more than Red Rose Tea.

So yes, Canada is not forever.  While America is strong, Canada will be strong but the future is more centripetal, breaking into new alliances not based on geography.  This may be more successful than Canada today, despite Canada being pretty much the best place on earth as it is.

(1)  See some Stratfor examples of how geography is destiny: China's position and Brazil's position. There's a simple one for Canada too.