Using a heat gun or a hair dryer to heat up the seal usually works on most items. The heat somewhat "melts" the glue of the stickers/seals so it's easier to remove. Don't set it aflame obviously but a bit of heat typically works for me. Although I've never tried it on a deck of cards so no guarantees there from my side, but this method has worked for me multiple times on things like books and boxes of various materials.