The citizens in the Great White North were the first in North America to get the official reveal that they would get the Samsung Galaxy S III smartphone (the US had to wait a few days later for their own official announcement). A large number of wireless providers in Canada was supposed to start selling the Android 4.0 based smartphone starting this Wednesday, June 20th.
That was then; this is now. According to a Twitter message from Samsung Canada, "Due to unprecedented demand, our launch of GALAXY S III will happen June 27th, rather than June 20th. Thanks for your understanding." This would seem to indicate that pre-orders for the smartphone have perhaps been much bigger than Samsung had anticipated.
The US launch of the Galaxy S III was supposed to happen with five wireless carriers in June as well but it looks like Verizon won't be shipping the smartphone until July 10th, according to Droid Life. US Cellular has also indicated they won't ship their version of the smartphone until sometime in July. So far, Sprint and T-Mobile are still targeting a June 21st launch date for the Galaxy S III for their networks. AT&T claims it will start shipping the phone on June 18th.
Source: Samsung Canada Twitter page