What type of sealer/stain to use on untreated cedar 4x4 lumber glued together
I'd go to the manufacturer of the wood glue you want to use before you get too far along.  Titebond is popular and I've had great luck with it, in their FAQ they have specific instructions for gluing up cedar, before you finish it, due to the oil in cedar.  

I think most of them are pretty oil resistant once they cure, especially polyurethane, which is pretty much impervious to everything, which is why it's awful to get on your hands.  Cleans off like a tattoo.  But polyurethane is a mess to work with, and where it gets on the work surface, you're going to have to sand it off, and it may soak in a ways.  No stain or sealer will get past the polyurethane.  

Tung oil is very good stuff. I worked for a contractor years ago that did a lot of cedar decks.  He liked a mix of turpentine and boiled linseed oil, which was considered old school even back then.  Tung oil seems to harden a lot better than linseed oil.  I'd prefer it over polyurethane for a work bench.  I wouldn't stain a work bench.