Celine Dion was in the audience for a change — to cheer on one of her former opening acts. The “My Heart Will Go On” belter introduced impressionist Andre-Philippe Gagnon over the weekend at Las Vegas’s Venetian hotel-casino, then watched the show with her husband, Rene Ang lil. Gagnon toured with Dion for two years as her opening act, but the two have known each other for more than 15 years (they both debuted in Montreal at about the same time). “We come from the same show business world,” Dion told the Associated Press. Dion and Angelil are producing Gagnon’s show.