WARNING: This page is about a different car, the 2006 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Sunroof View
Courtesy of GENERAL MOTORS CORP.
Remove the roof lift off panel.
Fig 2: Removing The Weatherstrip From The Weatherstrip Retainer
Courtesy of GENERAL MOTORS CORP.
Remove the weatherstrip from the weatherstrip retainer.