Yep, Shellac is sometimes called the universal primer. I have heard that Polyurethane can have problems but others say it works fine. Dewaxed shellac is probably better than the rattle can stuff. Seal coat is a dewaxed shellac based primer but I have never seen it in a spray can.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.