Amanda Seyfried is dreaming up her ideal cast for Mamma Mia 3 - and her vision includes Sydney Sweeney. "Sydney Sweeney could show up," Seyfried, 39, told Entertainment Tonight while attending the 16th Annual Governor Awards in Los Angeles on Sunday, November 16. "There's a bunch of girls that really want to be a part of it, and I'm all for it." Seyfried and Sweeney, 28, costar in The Housemaid, the upcoming Paul Feig-directed thriller due out in theaters on December 19.