I'm sorry, but i can't seem to find it anywhere. How many range increments can a cannon attack at the touch AC? are the considered early firearms for that case? I can't seem to find confirmation
The cannons in Ultimate Combat? As far as I can tell, they target normal AC, not touch. The only cannons listed are direct-fire weapons.
A direct-fire weapon uses a normal attack roll, with the normal penalty for nonproficient use.
Normal attack rolls target your regular AC, not touch.
unless i'm wrong, they're considered firearms
They are in a different section of the book, not with the firearms rules. Unless they specifically say that they are treated as firearms, they are not firearms.
Edit: Ah, wait. The firearm rules do have this:
Firearms are further divided into one-handed, twohanded, and siege firearms. As the category’s name implies, one-handed firearms need only one hand to wield and shoot. Two-handed firearms work best when you use twohands while shooting them. Two-handed firearms can be shot with one hand at a –4 penalty on the attack roll. Siege weapons are typically mounted on some sort of platform, movable or otherwise, and have greater power but a much slower rate of fire—they’re detailed in their own section, beginning on page 158.