The pair will live as travellers in the region of Goa to prepare for the film, in which Diaz plays a neurotic American whose life changes when she meets an English traveller (Winslet). Jack Black will also star.
A source says, "Cameron and Kate have met socially but have never worked together.
"After they signed up for the movie they got talking on the phone. They decided the perfect way to prepare for their roles would be to go backpacking."