Amanda Seyfried Explains Why Sydney Sweeney Would be PERFECT for Mamma Mia 3 (Exclusive)

Amanda Seyfried chats with ET on the premiere of her new movie, ‘The Housemaid,’ which hits theaters Dec. 19. The Oscar-nominee explains what drew her to the movie, why her co-star, Sydney Sweeney, could be good for a job in ‘Mamma Mia 3’ and the way she plans to have a good time her fortieth birthday this week