There's a Rolling Stone article on Ry Cooder from years ago in which Dewey Balfa said that after he lost his brothers Will and especially Rodney, he almost gave up music entirely. But when Ry Cooder, the musical director of the film, had him play in the movie, his spirit picked up and he continued to perform another dozen years. So, in a way, that film was important to the continuation of traditional Cajun music.
They don't often get Cajuns right in the movies. David Straithairn does a good accent in Passion Fish. And Adam Hebert is playing in the background of a Charles Bronson-James Coburn picture, Hard Times. I think there is a Nathan Abshire song in the Paul Newman movie The Drowning Pool.
This should start you on the right foot: NFB, National Film Board of Canada. when you do a search on their site, type in "Acadian exile",as they have 2 long documentaries on the subject.
Then there is the CBC. witch is the Canadian Broadcasting tv in Canada and witch has done "many" documentaries on the subject.
Enjoy your search, at lest this is a good start I hope.