As a European who has toured extensively in Canada, maybe I have some perspective on this.
my biggest Canada/US tour was a two-month loop from Toronto through Ontario and Quebec to the Atlantic (Gaspe) and back via New England and upstate New York. At no point was I bored. I do have some sympathy for your attitude to the prairies, though; my original plan had been a coast-to-coast ride, but I ditched that because day after flat day struck me as less interesting.
I find that motivation is never a problem for me on tour. Solo touring is meditative, it's like an exercise in mindfulness. One becomes attuned to the rhythms of the ride, aware of one's surroundings, often not thinking, just being: it's a very zen-like state and the opposite of boring. And I tend not to plan routes in too much detail. I have an idea where I might end up that evening, but am content to explore byways along the way and change my plans altogether if somewhere or something looks worth investigating. On longer tours I am living very much in the moment - riding the bike doesn't feel like a holiday activity, being a cyclist just becomes my primary raison d'etre.
Try it.