Unless you have canvas for free, I agree with Paul and go synthetic. Canvas is just about never used anymore. It weighs a ton and rots and.. you can't heat shrink it and it's tough to pull tight.

If you must - people used to use house latex paint which has much more elasticity than enamel. Enamel will end up with cracks. Almost all canvas covered kayaks rot out at the coaming where water gets trapped.

Frames almost never rot. Boiled linseed oil thinned down is the common choice. If
you plan on putting a solid boiled linseed coat, plan on waiting about 4 weeks for it to dry. I don't think you gain anything by doing that. You want the preserving liquid to go into the wood. If any rot was to occur it will be in the mortises or around the coaming. The gunnels, ribs, stringers, beams never rot.