Charlie,
I'm not sure what the "best" canvas is but you need to decide what weight you want, whether it is preshruck or not, and if it is treated with a mildewside or not. I suspect that most folks who fix-up a canoe or 2 just get the std stuff from one of the Pros that sell material.
I checked and it is Rollin at Northwoods Canoe that I get my supplies, he only sells/uses the top line materials. He is linked on the Builders Directory, and/but, there may also be a Pro located close to you that would/could also sell materials.
Also, remember that you will also need things like tacks, staples, screws, stem bands, seat/thwart fasteners, varnish, filler, paint and bedding.
Some of these things are readily available at marine suppliers, like varnish, paint, bedding, screws, but others are easier just getting from a Pro.
Dan