Yellowcard, I don’t know about the “best stuff”. I have refinished the bottom of a couple worn and UV faded TuffWeave canoes, and a couple vintage glass & nylon boats by lightly sanding the bottom, rolling & tipping a coat of epoxy resin, letting that cure for a week or so, wet sanding the bottom and finally rolling & tipping a coat of spar urethane.
The boats came out looking like new, and have held up well over the years.
I suppose that could be cut down to a single step by using an epoxy resin with UV resistance. West 207 hardener has UV inhibitors, but I have never used it for that purpose.
For a Royalex canoe I would not go whole hull hog. If the damage is mostly restricted to the stems I’d add Dynel skid plates, or on a worn vee bottom possibly a full length skid at the apex of the vee, and I’ll be doing that soon to a well work ‘70’s Explorer.
Otherwise I’d scribe a mark near the waterline and paint the bottom with a couple coats of topside paint.
Badly scraped and scarred Explorer with scribe line.
P6130015 by
Mike McCrea, on Flickr
New white-on-white bottom.
P6160010 by
Mike McCrea, on Flickr
You could use a hull matching topside paint, or go two-tone with a different color.