When was the Montreal merger?

In short 2002

Here is a snippit from Wikipedia's page on Montréal

"Montreal was merged with the 27 surrounding municipalities on the Island of Montreal on January 1, 2002. The merger created a unified city of Montreal which covered the entire island of Montreal. This move proved unpopular, and several former municipalities, totalling 13% of the population of the island, voted to leave the newly unified city in separate referendums in June 2004. The demerger took place on January 1, 2006, leaving 15 municipalities on the island, including Montreal." - http://en.wikipedia.org/wiki/Montreal