I use shellac a lot in general woodworking. I almost always use dewaxed shellac. Usually it's right next to the shellac on the shelf. The can I have says Zinsser Bulls Eye SealCoat Universal Sanding Sealer, then way down at the bottom, 100% wax-free shellac. My reason is varnishes might not stick to waxed shellac. I had that happen once. Otherwise, shellac should be good at bonding to the old stuff in the canoe, and varnish should stick to shellac. The can even says Guaranteed Under ALL Clear Finishes. The dewaxed stuff is thinned out more in the can than the waxed stuff, so read the label. Generally I don't see this dewaxed shellac advice mentioned for canoes, so I might be wrong here.
I didn't do any staining. A lot of my new wood is next to other new wood. I sanded or scraped the old stuff in small sections when I had a little time. So I may have hundreds of hours of work in that but it wasn't all at once, so it wasn't overwhelming. New wood will darken some with sun exposure.
I used Epifanes gloss varnish. I have a book on finishing that wasn't enthusiastic about polyurethane's UV resistance, even if the label says spar varnish. Epifanes uses phenolic resin, tung oil and UV lots of inhibitors, all stuff you want. I have seen negative reviews but everything has negative reviews. The can instructions suggest seven coats, the last 5 at full strength. I gave up after six coats, and I had a hard time brushing it at full strength - like brushing maple syrup. It took me a couple of hours to lightly sand between coats, maybe an hour to put on a new coat, and that's only the interior, not inwales, thwarts, seats or decks. Right now it is extremely glossy. In a couple of weeks, it should be hard enough to use fine steel wool to cut the gloss a bit. I used about 1500ml so far, or 1.5 quarts in 'merican. After I was done I read that the thinner I used, Home Depot Odorless Mineral Spirits, isn't a good idea for thinning Epifanes. Seemed to work for me but probably the cheapest possible thinner is a risk for expensive varnish.
IMGC4914 by
Dave, on Flickr