SpoilerTV has a couple of 24 season 8 promos up. There is a fleeting glimpse of Callum.
Do not click the link or the cut unless you want to be spoiled.
From the scene by scene recap of the promos on SpoilerTV:
Russian mobster (played by Callum Keith Rennie) is pointing a gun to Renee's head on a rooftop. Renee screams out "DO IT!" (oh hell no!)
We all knew something like that was coming, right?