Bioware has confirmed that Anders will be one of Hawke's companions in Dragon Age 2. That part's not very surprising. The surprising part, after the break, is who's coming along with him.
One of the companions in Awakening, Anders is a rebellious, and somewhat aloof, mage with a penchant for escaping the Chantry and winding up in the Templars' grasp again. As the Warden Commander, you had the option of conscripting him into the order and then helping him find his phylactery.
Anders can be found in Kirkwall during Hawke's journey tending to Fereldan refugees in the slums, but he's brought a friend with him as well - another Awakening companion.
Anders, the light-hearted rebel mage from Dragon Age: Origins, Awakening, has changed. Urged by his friend Justice to fight the Circle of Magi more actively, Anders agreed to become Justice's human host… only to find that his anger at the Circle warped Justice into the demonic spirit of Vengeance. Now Anders must struggle mentally and physically to maintain his control over the demon within... at least long enough to see the Circle of Magi overturned forever.
For those who hadn't played the expansion, Justice is a benevolent and rather stiff spirit who was forced into the physical world and into the body of a slain Grey Warden. You could also recruit him to your cause and show him that the world of Thedas was not as inconsequential as Fade residents regarded him as. From the looks of it, however, neither character will be the same as you remember.
How this will play out is being held relatively close to the chest by the writing staff, but it appears from the description, along with screenshots, that you'll be interacting with two characters - normally the mage and, when his eyes go all Illusive Man, the transformed spirit within. It may also be possible to push Anders from one side to the other more gradually as you may be able to either soothe his desire for revenge or egg him on.
Being the Jade Empire fan that I am, my mind instantly raced to the spirits fighting for control of Wild Flower. So yeah, allow me to take a moment to SQUEEEEEEEE!!
Anders' character page can be found here.