I think a young Whitney should be someone with model looks. Whitney had the look of a model and a presence that would light up any room. The part should go to someone new with similar attributes but a person that will be skilled enough to carry the role. I don't think singing is necessary since no one sounds like Whitney. When Tina's movie came out Angela Bassett could not sing and looked nothing like Tina yet she was able to portray Tina's presence (naive at first, scorned, and then a woman in control of her destiny) very well.