language variants

I am creating a Canadian national project site in English and French. Given that French Canadian (fr-CA) has had few translations done, we're going to use standard French (fr).

However, for those browsers who have languages set to fr-CA, we don't want to display the site default/fallback language of English, but the fr (French) version of the pages.

I'm sure there's must be a way to set Drupal so the fallback for fr-CA language is fr, while the site fallback remains English, but I've been unable to locate it in the documentation.

Any help would be appreciated.