Genie is the fast-talking, scene-stealing funny man. Your Genie doesn't need to be the strongest sing and dancer - the ability to do comedy is much more important. Cast a naturally funny actor that will make this character his or her own.
Princess Jasmine should be cast as feisty and rebellious, yet genuinely sweet and somewhat naïve. Jasmine is a future leader with strong opinions on how things should be done, and the audience needs to see this side of her as well as the side that Aladdin falls for.
Iago is another great comedic role. Like the Genie, he or she need not be the strongest singer, but comedic skills are a must. Iago has several sarcastic jibes and asides.
Jafar is the villain. In order to portray this through casting, consider a taller boy with a changed voice. His songs will not only be more effective, but a deeper voice will help convey Jafar's menace.
The Sultan should be able to play a father figure convincingly. Although a bit scattered, he needs to be able to portray love and care for Jasmine.
The Narrators (5) can be any combination of boys and girls. All should be able to sing well and speak clearly since they are responsible for setting scenes and advancing the plot.
The Guards, including Razoul, need not be the strongest singers. Cast students with good comedic skills who can carry a tune.
The Ensemble consists of Townspeople, Shop Owners, a Baker, a Matron, Harem Girls, etc. They should be good actors who sing well, as they are featured in all of the production numbers.
The Magic Carpet works best when treated as a character in the show. Rather than a platform on wheels with no personality, having two actors puppeteer the Carpet adds much more fun and creativity. Details on how to create and manipulate the Magic Carpet can be found in the Props section of the Director's Guide.