AAA has some reasonably decent maps of Canada (and provinces and cities) free if you're a member. I think nonmembers can purchase individual maps, but I'm not absolutely positive about that. Their map of all Canada is handy for overall planning.
You should be able to get maps also by writing/calling/emailing the various province's tourism department or whatever their equivalent is. As I recall, Manitoba, Saskatchewan, and Alberta had pretty nice maps (and probably Ontario, too, though I don't know if I picked one up); Yukon had a perfectly usable one, though not quite so nice (and there really aren't that many roads to worry there anyhow); and the only free BC ones from the tourist info centers were for the territorial parks and were divvied up into about a half dozen regions, each with their own map, which was nice for finding the parks but not quite so nice for planning a substantial trip. The BC park ones were not quite so complete in terms of which roads they had, too.