©Courtesy of Universal Pictures Amanda Seyfried has confirmed that “Mamma Mia!3” is going to be made! Seyfried and Meryl Streep were cast in the jukebox musical directed by Phyllida Lloyd, with Sophie Sheridan played by Seyfried and Donna Sheridan playing by Meryl Streep. It was followed by 2018’s Mamma Mia! Here We Go Again. There has…