Both sides of this argument are being intentionally dense. PLEASE STOP
IT.
Side 1: The RULES
AS WRITTEN allow you to pick a unit you can see, then pick a range at which your cannonball starts it's path of carnage.
Side 2: When you intentionally choose a range which cannot possibly hit the named target, you are not actually targeting that unit.
Using
RAW, there is TECHICALLY nothing wrong with overguessing. This is however, the worst kind of

.
This could be solved with a rule (either in the rulebook or a house rule) that if the cannon shot misses the named target (i.e the path of the cannon ball after land+bounce doesn't impact the named unit) then it misses all models it would have otherwise hit.
After 15+ posts on this topic, hasn't it become painfully obvious sides have been taken and no one is moving from them? Let's move on, shall we?
Viperion