is the title character and therefore carries most of the show. You'll want your most charming, best singing and best acting student for this role. He'll need the versatility to play the funny, slick prankster as well as the romantic lead.
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.