i usually use tung oil finish for my bows but when i used burlap it was a challenge getting it to work on the burlap. on one of my burlap backed bows i used shellac, and it was pretty simple and turned out ok, although shellac isnt my favorite finish by far. i suppose one could use a spray poly over linen or like pat said tru oil or tung oil with enough coats. i found with burlap a sponge brush brushed across the limb instead of down helped get more finish down in between the burlap than using my finger or going down the length, at least for the first few coats to get good coverage.