If the equal distribution of party roles is true, my guess is:
Mage: Viv, Solas, Dramatic Hands Mustache Guy
Rogue: Sera, Varric, Cole
Warrior: Cassandra, Iron Bull, Grey Warden
I really would like Cullen to be a companion, cos I think we're getting a ton of mage viewpoints (pro circle, apostate, and I'm gonna just guess Mustache Guy will be Tevinter), but not very many Templar viewpoints. But I also see the value of both a Qunari and a Grey Warden perspective. Really, I kind of think the rogues need to get a lot more interesting.
I'm also going to hope that somehwre there's an either or companion - like Bethany/Carver, Alistair/Loghain, Kaiden/Ashley. It makes things more interesting. In which case, I have no idea, but my gut intinct would be Cassandra/Cullen.
I just really don't like non-companion romances, they just feel tacked on to me.