Sure, but those usually have a gun shield protecting the gun crew & it is done due to the gun barrel being long & the gun being heavy, so it is better to mount it on a single point, instead to jave it traverse on a curve (which is not a problem for an archer).
Not that the apertures are stepped instead of smooth - I guess the avoid the funneling effect mentioned above, possibly changing a near miss to deflection and hit on the gun shield. Should not happen if the steps get in the way.
Apparently not [0]. IANA cannon expert but I think in the 18th C their biggest threat would have been from cavalry rather than sharpshooting infantry or precision fire from other cannon.
