I don't think sealer is the right term but I used a "sealer" a few years ago to help the stain work properly on some pine that was large grained. I don't remember the brand name now but I think it cam from Minwax. Check with your local box store and see what the stain mfg's recommend for pine. That may work for your application as well.
Tools are like guns, You can never have enough.
Where did I put that tape measure???