The EOSHL became a sanctioned Senior "A" league in 2003. In 2005, the league was promoted to Senior "AAA" to compete against Major League Hockey and have a chance to win the Allan Cup. In 2006, the league dropped from 6 to 4 teams.
During the 2007-08 season, a new team known as the Cooks Bay Canucks joined the league. What ensued with this franchise his quite original, as the team, although successful on the ice, underwent two name changes in the same season. The team started the season as the Cooks Bay Canucks, but soon dropped it for the Simcoe County Canucks. Although that does not sound too strange, the Canucks made the playoffs and before game two of the league semi-final announced another name change to the Simcoe County Tundras, with new logos, and completely different jerseys and team colours.
In May 2008, due to major team losses in the Western league leaving the Western League with two teams, the EOSHL and the MLH merged to operate as Major League Hockey.