The Canadian national parks in the Rocky Mountains are very popular (and for good reasons). Banff National Park had 3.3 million visitors in 2012-2013, and Jasper National Park had almost 2 million (Source). Although only a fraction of those visit backcountry campsites, a fraction of >5 million is still a very large number, and therefore reservations are required.
Those statistics are not specified by season. I suspect that visitors are highly concentrated in the summer. I enjoy backcountry hiking, but I seek solitude. As I don't mind cold or waking up with half a decimetre of fresh snow, one alternative could be to go very late in the season. How late in the season, if ever, do backcountry campsites in Banff, Jasper, Kootenay, and Yoho national park, and the adjecent provincial parks, grow quiet? By quiet, I mean an expectation value of less than one tent per backcountry campsite, or, in other words, that I would have a 50% chance to be alone at any given backcountry campsite. Does this happen within the season that hiking (as opposed to skiing or snowshoeing) is possible at all?