In the case he's bi, be prepared for the bash about it because 'he was obviously straight in DAO'.
Honestly, as someone who is going to romance him as a straight female warrior, I really don't care if he's bi and don't see the problems with him being so. Heck, my best friend in the entire world who is also bi is currently dating a guy, that doesn't stop her from being bi, it just means she's in love with a guy at the moment. This is all I'll say on this sexuality preference as I usually deviate from it, but know that I support whatever he ends up being as I feel sexualities shouldn't be blown out of proportion. If people don't like that he's bi? I'm sure there is a straight option that they could consider. In DA2, I wasn't attracted to any of the LIs and my Hawke ended up single, even. That's an option as well. All I'm saying is that I'm at least glad that Bioware is putting the characters first and that most of us shouldn't be so quick to judge and jump wagon before even playing the game. For all we know, it may end up that their romance arc sucks, or that we may absolutely love their character to the point that we think: hmmm I usually don't do this but I think in my next play through I'll roll a (insert gender/race character) and try this person. Anyways, peace, love and happiness. That's all I wish to say on the issue as, again, the topic of sexualities can become explosive. You are free to completely disagree or disregard my opinion, which is fine.