There is choice China, partly because there is necessity, and partly because of metacognition. Many animals besides humans must make choices. They must choose when to stalk prey, which prey to stalk, when to give up the chase. Their reasoning can even go out the window when circumstances are unfavourable, and then they make more risky choices. These are choices made based on necessity. Thinking about thinking on the other hand, that's metacognition, basically what we're doing with this thought experiment.
Of course there are actions which are out of our control, that's a peripheral nervous system. You don't choose to sense something, your body responds to stimuli. You choose to look towards the screen, but you don't choose to breakdown the signal your eyes recieve into the biochemical processes that you eventually perceive as English words on the CanadianContent forum.
Your thoughts don't identify directly with the sensations, but rather with the perception of those sensations. You and I may look at the same object, and perceive it as a different colour, even though we sensed the same object. Choice only enters the picture after your body has filtered and processed these events. An example, did you really just see that, or is your mind playing tricks on you?
Thought is subjective, and that is a consequence of the inhomogeneities between sentient beings. Your brain has created different models of the same world that mine has. We haven't experienced the same viewpoint of the world. If you were to inherit my sensory organs through a transplant, would you then perceive the same world as I would? No. You would sense as I would, but your brain will decipher it differently based on your past experience. That's because your percepts are different from mine, and they shape the model your brain uses to decipher new information.