Fontaine was drafted by the Toronto Argonauts in the second round of the 2005 CFL Draft but re-joined Kentucky for his senior season. He signed with Toronto on May 17, 2006. As a rookie, Fontaine played in all 18 games and made appearances at special teams and linebacker. He led the Argonauts and was second in the CFL in special teams tackles with 23. In his debut on July 6, 2006, he dressed as the backup linebacker and made appearances on special teams. He recorded his first defensive tackle in week 6, where he was in the game in third down and goal line situations. Against Calgary he led all players with three tackles. During the 2006 playoffs he appeared mainly on special teams, recording two tackles in the East Championship game against the Montreal Alouettes. After the season, he was named the Argonauts rookie of the year.