Clear polyurethane products are relatively cheap and readily available for purchase, and can serve as a sealer to prevent bubbles from rising from the wood when TotalBoat TableTop Epoxy is applied over it. These products will form a decent bond to the wood when used as a wood sealer prior to applying epoxy. In comparison, using a very thin layer of epoxy as a seal coat will provide a much stronger bond to the wood than a polyurethane, though it will take much longer for the seal coat to cure.
It is strongly advised to perform a small test sample to verify that the desired method of sealing the wood then coating it with epoxy achieves the desired results.