No real sure they are cannon balls? If they are you made out like a bandit ! If you post them in the What is it section on here you will get some experts on it and a positive I.D.
Good luck! Hope they are ok if not you are not out much
The mold seams would make them suspect, I agree with the others. Artillery projectiles had to be manufactured to near precision. A 6 pounder projectile would need to measure at 3.67 inches in diameter.... a 12 pounder at 4.62 inches.