I'll second Pappy's reply on steaming. When Gary and I first started working with steaming wood several years ago, we discovered that the wood didn't cool as quickly when the finish was on it. Therefore, it gave us more time for straightening and clamping. And again, we also found that it helped prevent checking. It was frustrating to see wood that was seasoned for several years, suddenly check after steaming. When sealing the wood prior to steaming, the checking was greatly reduced if not eliminated.
Yes, you can steam without sealing however, we found the results were better and we had more time to manipulate the wood. Try thinning your poly a bit with paint thinner. It may be easier to remove. Or, I've heard that shellac scrapes off easier. Maybe someone can chime in on that...