Given all the work involved, the materials, skills needed for it to
come out right, the fact that sanding fiberglass isn't the most
pleasant or safest job without good breathing eqpt, etc, I'd think long
and hard before deciding to do this.
If it was just a couple of small repairs, it would be one thing, but to
patch and then resurface the whole bottom is a big project. I'd see
what used canoes go for first.