Dan Aykroyd and James Brown appeared together in The Blues Brothers (1980), Doctor Detroit (1983), the Super Bowl XXXI (1997) halftime show, and Blues Brothers 2000 (1998).
When James and The Flames go onstage to perform their rendition of Caldonia, the music used was an actual recording of the real James Brown's rendition. The original includes a horn section, which was removed because the Flames didn't yet have a horn section in the film.
The film had been in development since 2000.