With the exception of Genie Aladdin had pretty much all its original cast, so did TLM I believe.Although, they did get Eartha Kitt, Patrick Warburton, and John Goodman (second season) back for Emperor's New School.
As for sequel, it could be something bringing Edward and Nancy back into the real world, or it could flip the idea and have real people going to the animated world.
I don't see a prequel film really working as Giselle hadn't even met Edward, it would basically be Giselle and Pip. It would be great as a series, but as a film it wouldn't have any romance or character interaction. Or they'd have to play it very carefully and never have the lead characters meet.
A series would work as they could have Giselle and Pip doing there own thing and Edward hunting trolls and seeking his love but being foiled by Nathaniel and Narissa. I can see that working as an animated series, but I don't see it as a feature film.