AnyNet is Samsung's version of CEC. - Roku's dont support incoming CEC (they dont allow other devices to control the Roku via CEC).
If you normally press a button on the Roku remote and it switches your Samsung TV's input to the Roku one, there is probably an issue with AnyNet on your TV (it may be disabled).
Try restarting your TV, or powering it off for a few minutes and powering it back on, then try again.