Overall a very achievable concept, sounds good! Some aspects of the concept document still sounded a little not-confirmed, so I would encourage you to investigate some of your ideas a bit more by going through the game modelling process taught in the unit and see what is most feasible to look at.
Some inspiration could also be drawn from games like Angry Birds.
Overall the concept sounds fun, and it would be interesting to see what the different cannonball types are like.