Jason provided the voice for the character of Denahi in Disney's 2003 animated feature Brother Bear. The film was the third and final feature created at Disney's Florida Animation Studio, which closed in 2004 as Disney decided to concentrate on computer-animated films.

Brother Bear told the story of Kenai (voiced by Joaquin Phoenix), an Inuit boy who kills a bear only to be transformed into a bear himself. When Kenai's brother Denahi sees a bear instead of his brother, he assumes that the bear killed Kenai and sets out to get revenge. To survive, Kenai must befriend a bear cub named Koda and learn the true meaning of brotherhood.

Brother Bear also featured the vocal talents of D.B. Sweeney as Sitka, Kenai and Denahi's eldest brother; Jeremy Suarez as Koda; Michael Clarke Duncan as the grizzly bear Tug; Joan Copeland as Tanana, the spiritual leader of brothers' tribe; and SCTV alumni Rick Moranis and Dave Thomas as moose buddies Rutt and Tuke. Phil Collins provided six songs for the film.

Coincidentally, animator Ruben Aquino, who served as the supervising animator for Denahi, had supervised the animation of Adult Simba in the film version of The Lion King. In the film's production notes, Aquino explains, "Denahi was an interesting character because he goes through so many changes during the film in relation to his state of mind and appearance. In the beginning of the movie, he's very happy-go-lucky and enjoys horsing around with his younger brother. When Sitka is killed by a bear, Denahi becomes more somber and sad. Later, when he thinks Kenai has met the same fate, he becomes angry. There is a lot of emotion, a lot of pantomime. Throughout most of the movie, Denahi doesn't even speak; so the challenge is to make the audience know how he's feeling through his actions and facial expressions. As the story progresses, he becomes more and more savage and driven, which is reflected in his costumes and hair. Jason Raize gave us an excellent vocal performance to work with."

Disney released Brother Bear in theaters on November 1, 2003. A 2-disc DVD release followed on March 30, 2004, which includes full-screen and widescreen versions of the film. A documentary on the widescreen disc includes a section on the film's vocal talent which briefly features Jason.