Lightweight Map of Canada?

Not as light as possible, but pretty light and really cheap: Get regular maps for all the provinces along your route for free through a member of the US AAA or the Canadian version. Laminating can be done really cheaply with package-sealing tape. I do this on regular paper to make little reference cards for my wallet and they last for many years. Then cut out just the routes you are going on. 2 or 3 inches wide, and the weight won't be much.

Pro-tips: annotate where the side roads lead ("Winnipeg, 45 km"), campgrounds, attractions, etc before trimming to a narrow width. And cut the km scale from the legend and reposition it in the middle of a wheat field in Manitoba before applying the tape so it is fixed to the map section you will bring with you.

"Wheat Field in Manitoba"

I think that's most of Manitoba. Thanks for the suggestion, I figured I could pick them up for free but I know the "good" maps like to throw in saucy special features like national parks guides and stuff like that. National Geographic's maps look pretty good, rip-proof and water resistant paper is lighter than laminating.

Will probably use your suggestion as the fallback, ergo, 90% likely that's what I'll do.