I dont think this fight would go much time on the ground. So standing, I dont think Werdum can (T)KO Cain. Cain, however, has power to (T)KO werdum.
Cain is stronger and faster, but werdum has size advantage and his striking has improved a lot. He might take it in the scoreboards. If he takes the early rounds, then Cain would be obligated to engage him a little less carefully and werdum might capitalize on that by scoring more points and/or taking Cain down. Werdum's cardio is another issue to keep in mind.
I would give the edge to Cain if they fight, but could see werdum taking it by points.