It's definitely the early gun, they had a very distinct curved mantlet with both the flanges on the side of the cannon barrel and a notch on one side of the bottom edge, and the newer guns had that large muzzle brake on them.

What's harder to tell from that angle is whether it's an M4A2 or some other variant. I think it's the A2 based on the little piece of metal that goes all the way around the neck of the turret on the body there, but the best way to tell would be a quick look at the front corners. The A2 and newer tanks had a welded body with a sharp corner and easily visible weld lines where the front plate meets the side, while the first Shermans had a full one piece cast steel body that had curved edges to it.