Yes, a third Roger Rabbit NOVEL is coming out November 29th, exclusively as an e-book, by Roger's original creator Gary K. Wolf (that's him as Eddie Valiant on the cover).
The Roger Rabbit of the novels is quite a different character, though since the movie "adaptation" there has been some attempt by Wolf to make them more similar. In the first novel, Who Censored Roger Rabbit?, Roger is murdered and his doppelganger - a self-generated temporary stunt double - must solve his murder with Eddie Valiant's help. This Roger is the star of newspaper comic strips rather than cartoons, and talks in speech bubbles. Not to spoil, but he is also far less of a good guy than any Disney animated hero gets to be.
Knowing a good thing when he saw it, and understanding the public's desire for a sequel, Wolf retconned away Roger's death in a second novel, Who P-P-P-Plugged Roger Rabbit?, which used the Disney versions on the cover.
The new novel features actor Gary Cooper as a major character. With Bob Hoskins now retired from acting, a theatrical sequel seems less likely than ever - but should Disney ever lose the rights when Hell freezes over, I'd love to see the first book get an accurate reimagining.