Toni Collette and Cameron Diaz are on-screen sisters who seem like the real deal.

Reunited in Sydney to promote their new film, In Her Shoes, the actors giggled, held hands and finished each other's sentences, just like siblings. "I have a sister and she (Toni Collette) has two brothers," Diaz said ahead of the film's Australian premiere in Melbourne tomorrow. "We understood those roles and those dynamics." In Her Shoes tells the story of sisters Rose (Collette) and Maggie (Diaz) who fall out over a guy and embark on a journey of self-discovery.

Rose is the professional, responsible sister while Maggie is screwed up and irresponsible. "Maggie is this kind of bright shining person who you learn is quite empty and scared of what she has or doesn't have inside," Collette said. "And Rose is the opposite. Her internal world is quite rich and her external world is what is lacking." Directed by Curtis Hanson, the man behind films such as 8 Mile and LA Confidential, In Her Shoes also stars Shirley MacLaine as Rose and Maggie's grandmother, Ella.

"The story itself is just so beautiful and easy to relate to," Collette said. "It is very human." In Her Shoes has been labelled a "chick flick", but both Diaz and Collette are quick to dispute this description. "Even if you are a man, you can relate to these issues," said Diaz, who dates American singer Justin Timberlake. "It is all relatable."

Collette launched her movie career with the role of Muriel Heslop in 1994s Muriel's Wedding. She put on 20 kilograms for that role and had to again put on weight for In Her Shoes, this time around 15 kilograms. "When you get such a great character and the story is so brilliant and the idea of her being overweight is so pertinent to her journey, then it doesn't really become a burden," said Collette, who is again back to her normal weight. "The weight is kind of representation of Rose's lack of self and overload of responsibility."

Meanwhile, Collette is well on the way to following in her husband musician David Galafassi's footsteps. The actor recently finished recording her first album with band Toni Collette and the Finish. "The record is made and I have a really fantastic band now," she said, adding that the album would be released next year. "It is alternative, rock, pop... there are some ballads in there. "It is melodic and kind of spacious." In her Shoes opens nationally on October 13.

- AAP