I think the Thunder know Cannady can shoot, but they haven't been willing to use him in regular game situations. Perhaps they think his size makes him a liability of defense. At those end-of-quarter situations after a timeout, they're just hoping to get him an open look for a three, since he probably is their best three point shooter.
Cannady is probably setting some type of +/- record per minute:
Game 1: +3 (0 minutes)
Game 2: +0 (0 minutes)
Game 3: +2 (0 minutes)
Game 4: +2 (0 minutes)