Baranski, the London daily says, will play Tanya, while Walters will take on the role of Rosie, both close friends of Streep's character Donna, whose daughter Sophie is getting married.
Baranski is a two-time Tony winner, the first for Mike Nichols' production of Tom Stoppard's The Real Thing, the second for her performance in Neil Simon's Rumors. The actress is still remembered as the hard-drinking Maryanne in the nineties sitcom "Cybil." Baranski most recently appeared onstage in the Manhattan Theatre Club production of Regrets Only.
Walters won a 2001 Olivier Award for the National production of Arthur Miller's All My Sons. On screen she played the dance mistress in the movie version of "Billy Elliot," a performance that brought her an Oscar nomination.
Joining Streep, Baranski and Walters on the "Mamma Mia!" film set – filming is scheduled to start in June – will be Pierce Brosnan as one of Donna's ex-suitors.
The movie will be directed by Phyllida Lloyd, who will be making her feature-film debut. Lloyd helmed both the London and Broadway mountings of the international hit musical. London's Daily Mail also reports that three songs from the stage show have been dropped: "Thank You For the Music," "Under Attack" and "Knowing Me, Knowing You." The movie, however, introduces another ABBA song to book and screenplay writer Catherine Johnson's storyline, "When All Is Said and Done."
Based on the back catalogue of 70s pop group ABBA, Johnson's plot tells the story of bride-to-be Sophie Sheridan, who hopes to discover her father's identity on the eve of her wedding. She brings three men from her mother Donna's past back to the Greek island they last visited 20 years previously.
The show and film features music and lyrics by Benny Andersson and Björn Ulvaeus. Since the original London production opened in 1999, the show has grossed over $2 billion worldwide.