"a quart (750) of primer goes under the 750 of paint and all that goes over a gallon of primer"... wait, what??? I'm not sure I understand this.
Steve - I agree generally with Zach and Dave on amounts, but it can't hurt to have a little extra to ensure good coverage and for later touch-ups if needed. The reason you're seeing imperial and metric measurements, I believe, is because many brands of finish come in quarts, but Epifanes, for example, comes in 750ml containers. Note that 750ml is only about 80% of a quart. In any case, your best bet is to have at least one can of paint, and 2 cans of varnish (especially if buying 750ml quantities). With a cedar-canvas canoe, you've got filler, then perhaps a glaze and/or primer, then paint, so your main goal for paint is good coverage and a nice smooth coat of paint over those other materials. Paint, wet sand, paint again until you're happy with your finish. On the interior, though, varnish is your full and complete finish. In the old days, manufacturers applied only a couple of coats of varnish, maybe over a coat of shellac, but on restorations I put on at least 5 coats of varnish, often many more.