After going undrafted in the 1995 NFL draft, Isaia was signed by the Cleveland Browns. As a rookie, he did not appear in any games. In 1996, he appeared in nine games. In 1997, he injured his knee and was placed on injured reserve on August 18, 1997. However, he didn't appear in another game until 2000.
On April 1, 1999, Isaia signed with the Indianapolis Colts. On February 17, 2000, he was signed by the Oakland Raiders. He was released on August 27, 2000. Three days laters, he was signed by the New England Patriots. In 2000, he appeared in all 16 regular season games starting 14. On May 15, 2001, he was released by the Patriots.
Isaia is of Samoan descent. His son Jacob is projected to be one of Hawaii's top prospects in the class of 2018.