Complex sentence: In 2003 the Canadian organization Fondation Émergence instituted a similar event, the National Day Against Homophobia, on June 1; in 2006, they changed it to May 17, to join the international movement.
Split into simpler sentences: In 2003 the Canadian organization Fondation Émergence instituted a similar event, the National Day Against Homophobia, which was held on June 1. In 2006, they changed the date to May 17, in order to join the international movement.