This is all speculation...
What I think will happen
Blackwall: Unavailable. Status as a Grey Warden would weigh down on romance prospects and is dedicated to the life being a Warden entails.
Cassandra: Available confirmed. Heterosexual most likely, but may be bisexual.
Cullen: Available confirmed. Most certainly heterosexual. I bet he's straight.
Dorian: Available. Homosexual. If Solas is homosexual, then Dorian would be the bisexual option to level things out. Or, he could be just heterosexual.
Iron Bull: Available, but I've a sneaking suspicion he probably won't be? Most likely Bisexual.
Sera: Confirmed available and romanceable by female Inquisitor.
Solas: Available. Bisexual, but sneaking suspicion that he may be homosexual. If Dorian's homosexual, then Solas may be bisexual to balance things out.
Varric: Unavailable, but due to popularity, maybe he'll return as a love-interest. Most probably will be heterosexual, though.
Vivienne: Available and bisexual.
Bonus: Cole: If confirmed as companion, he maybe available would probably a heterosexual option (hopefully not, hopefully a bisexual option, at least).
Heterosexual: 3
Bisexual: 3
Homosexual: 2
---
What I'm hoping for
Blackwall: Available. Bisexual.
Cassandra: Available. Bisexual.
Cullen: Available. Heterosexual.
Dorian: Available. Bisexual.
Iron Bull: Available. Bisexual.
Sera: Available. Homosexual.
Solas: Available. Heterosexual.
Varric: Available. Heterosexual.
Vivienne: Available. Bisexual.
Cole: Available. Homosexual. LOL Nope.
...Personally, I'm kinda hoping I could romance Cole as a dude inquisitor. Not expecting it, but I'm hoping!
EDIT; I haven't read Asunder and I didn't quite get what Cole was as a character, so... this raises quite a few problems.