They are lovely looking packs and the appeal of leather and canvas goes beyond practicality alone. I have no personal experience of Frost River, but regularly use canvas and leather packs I've made myself for day hikes. For the price point, when shipping and duty is factored in you should be able to get something that is actually hand-made for not much more. The build quality from FR gets excellent reviews, but if you are paying for leather and canvas you clearly have an appreciation for nostalgia and asthetics too, so you might as well go the rest of the way and get the best finish you can.
Further more, based in my own rxperience, for a rucksack unwaxed canvas is superior. Waxed canvas doesn't breath well in the heat and in the type of extreme wet where the waxed variant offers a small benefit, you're better off with a light weight cover, using waterproof bags to divide your gear inside the pack, or popping a poncho over you and the bag.