I have had good success with Helmsman Spar Urethane spray. The clear gloss comes very close to the look of the old varnish finish, and the semi-gloss does well on more modern guns. Quick and easy and durable. It also duplicates the finish used on S&W walnut grips.
The proper stain is more of a problem. For a reddish color like some of the old Winchesters, I like the No. 35 put out by Tapaderas (
www.tapaderaswinchesters.com). As it comes, it is too red, so I mix a few drops with Minwax Gunstock 231 stain until I get the color I want.
Jim