Richard Pryor's Widow -- Terrence Howard Should Play Richard Pryor

Richard Pryor's widow says Nick Cannon has NOT been cast to play the legendary comedian in a movie ... but she knows who SHOULD get the role -- Terrence Howard.

Jennifer Pryor -- who has some say over the decision -- tells TMZ Cannon jumped the gun when he hinted to us he had the part ... because the film's director, Lee Daniels, is still auditioning.

Pryor says it's an easy call ... she says Howard is perfect ... an intense, brilliant actor who has the chops for acting and comedy. But she'd insist on him losing some lbs.

According to Jennifer ... several other big names are also being tossed around -- Marlon Wayans, Jay Pharoah and Mike Epps.

Richard's kids are lobbying for Wayans. They've never seen eye-to-eye with Jennifer -- who was married to Richard twice. They've accused her of turning the film into a vanity project.

Jennifer says she loved Pryor immensely ... and if his kids can't understand that ... tough.