Zell---> Rikku (they have very similar smiles it's creepy,plus same hair color)
Quistis---> Seifer (interchangable)
Squall--> Paine (he's already a girl though)
Cid---> O_o ...(Let's not even go there) Okay let's go there...Queen Brahne minus the green/bluish skin color
Rinoa---> Garnet or Tifa (Garnet mostly, because their face shapes are more similar)