Doesn't look like a cannonball to me. Also, you give no size reference except some leaves. How deep are the holes? What is the diameter? I think it's probably some sort of counterbalance weight.
CannonBallGuy, where are you?
Skelly607, ordinarily I would need to ask for super-precise measurements of the ball's diameter (in hundredths-of-an-inch, like 4.52") and weight (in pounds and ounces) to tell for sure whether the ball is a cannonball or not. www.civilwarartillery.com/shottables.htm
But in this case, there's no need. Absolutely no cannonballs in any era of artillery history had raised numbers or letters on them. So, that ball definitely is not a cannonball.
Also, none had indented letters either -- and any with a indented number higher than 2 (such as 4, 12, 16, etc) are also definitely not a cannonball.