It seems that someone working for Vodafone in Australia let the cat out of the bag for the United States launch date of the Samsung Galaxy S III. According to a livestream media event from the Australian carrier, the SGS3 will begin its ‘nationwide US tour’ in New York on June 20. This is the same day as the Canadian launch, so this rumor is not too far-fetched.
Still, it is possible that this date is simply a moving target and might get rescheduled. There's no way to tell for sure, except to wait for the date, or for an official announcement from Samsung. We will keep you posted.
Source: S3Forums via UnWiredView