Chris Priestly posted a thread in the official Bioware forums confirming which of Hawke's companions will be romanceable throughout the game. Details (and spoilers) after the break.
From the forum thread:
Hello Dragon Age 2 fans.
Happy Valentine’s Day to one and all. We know many of you have romance on your minds today, so we thought we would confirm for you the potential romance characters in Dragon Age 2.
You can choose to romance:
Keep in mind that all Dragon Age 2 romances are optional, so you can choose to follow these subplots or not as you prefer. All four NPCs also have other non-romance subplots that you can again choose to follow if you want to learn more about these characters. To learn more about the romances, you will need to play Dragon Age 2.
So, if you are romantically inclined during your Dragon Age 2 playthroughs, you now know who you can pursue. Pitch your woo accordingly.
So, Varric's out as a love interest. Dammit, Dwarves always get the short end of the stick. Wait... I didn't mean that pun.
Anyways, you can check out the announcement thread here. Chris also posted some short stories written by the Dragon Age team that gives some backstory to the 4 romanceable characters. In particular, Anders' story is interesting in giving the duality between the mage and his newfound tenant.
Credit for the pic goes to Aimo, who shares my pain.