While Nate and possibly Anders are suitable for making an appearance in the game, I'm afraid they wouldn't be able to be full-time companions, as they'd both need to be back in Ferelden by the time of Awakening, which would be rather early in DA2. Of course, Mike might've meant temporary companions and not full-time ones, who knows.
As I see it, the best bet would be on one or more of the DLC characters (Silas, Sketch, Ariane, Finn or the Dace brothers) - that way, there's a chance to expand on largely untouched characters to sate the curiosity of those who played the DLCs, while at the same providing new characters for those who didn't. Plus, there aren't any plot deaths preventing them from making said return. The Dace brothers aren't very likely, as there would be little reason for them to leave Orzammar; Finn doesn't seem very likely either, it'd be hard to imagine him leaving the Ferelden circle; Ariane is a little more likely - it's not inconceivable that once she recovered the stolen tome she and her clan left Ferelden to join Marethari's clan in the Free Marches (though I wonder why the dalish would not move to the lands given to them after the blight); and Sketch and Silas seems the most likely, as we really don't know what happened to them after defeating Raleigh - though Silas said he wanted to serve the chantry (maybe by becoming a templar and getting transferred to Kirkwall?), and Sketch could've also gone to Kirkwall to get far away from Orlais (and subsequently getting captured and imprisoned in the Kirkwall Circle?)
Or, you know, they could screw our expectations and theories and toss in Oghren again, you never know

(truth be told, I really liked him, but story-wise I don't think it'd make much sense)