Bassey will sing the movie's theme song 'Guardian Of The Highlands' and Connery will voice a main character.
The two previously worked together on James Bond picture Goldfinger.
Sire Bill, created by husband-and-wife team Sascha and Tessa Hartmann, also stars Alan Cumming, Miriam Margolyes and Ruby Wax.
The film follows an ex-skateboarding champ living in a Scottish village who helps rescue an illegal fugitive beaver.
Connery is also an executive producer on the independent project, which is due to be released in 2010.