LATSET: Julie Walters and Christine Baranski have been added to the cast of Abba-themed movie musical MAMMA MIA! The respected actresses will join Meryl Streep and Pierce Brosnan in the film adaptation of the hit stage musical. Baranski will play Tanya while Walters will play Rosie, according to Britain's Daily Mail. Colin Firth and Stellan Skarsgaard have also reportedly been added to the film.