In Pixar’s Cars 2, Weezer performs the end-credits song “You Might Think.”
The song is a cover of the 1984 hit by the Cars. Weezer’s version appears on the Cars 2 soundtrack and plays over the film’s end credits, linking the sequel to the musical identity suggested by its title. The arrangement keeps the recognizable song while presenting it through Weezer’s alternative-rock style.
The original “You Might Think” was written by members of the Cars and became one of the band’s best-known songs. Its 1984 music video was also notable for its early computer-generated visual effects, though that video is separate from Pixar’s animated film.
The answer is Weezer, not the Cars, because the question asks who performs the version used in Cars 2. The Cars wrote and originally recorded the song, while Weezer recorded the soundtrack cover.