I’m still waiting for The Little Mermaid. I think Tom Welling would still make a great Prince Eric but I’ve recently seen a theory floating around tumblr that Ariel is Hook’s mom and that made me re-cast who Eric would be. So an alternative would be Richard Armitage. He looks awesome with guyliner and in leather (Robin Hood BBC’s Guy of Gisbourne).
As for Ariel herself, I’m not really sure. I used to think Sarah Michelle Gellar might make a nice Repunzel but I think she would be too old for the role now.