Yeah the Roger Rabbit is a miracle where multiple major studios came together and allowed their IP to be in the same work. Disney, Warner Bros, Fleischer Studios, Harvey Comics, King Features Syndicate, Felix the Cat Productions, Turner Entertainment, and Universal Pictures/Walter Lantz Productions all agreed to share their characters. One of Steven Spielbergs great accomplishments was negotiating this. With how protective these studios are about their IP anymore I doubt we'd see anything close to the Roger Rabbit movie sadly.

Not to mention some of the actors have passed like Paul Reuben who really sold the cartoon aspect of Roger Rabbit.

Roger Rabbit was voiced by Charles Fleischer. (Paul Reubens was under consideration in an earlier version, and you can find his voice tests out on YouTube, which might be what you're remembering.)