Hmm, not keen on Alba for that role at all. A very good actress, but not suitable IMO. Sue needs to be an unknown and a little more mature than 25, IMO. Unless they're going for an origin angle too but I feel they should use someone a little less beautiful or I'm going to be thinking twisted toyfare theater the entire time.
Count me as a non-fan of Jessica Simpson. Sure, she's attractive, but based on comments from the tv show, dumb as a sack of hammers. Which is not to say I expect actors to be MENSA quality material, but there's not much need for her to raise the profile of these movies, so why they'd go for her is beyond me. Find a Famke Janssen type to fill the role: a little less well known, capable actor, beautiful. I will say that Ms. Simpson fits the mental/comic visual image of Dazzler well though.