If the tripod head is marked "MX2000P" or "MX2000" inside the recess where the plate slides in, then you need the matching MX2000/MX2000P quick-release plate for that head.

That said, based on the community feedback, a replacement plate costs nearly as much as the tripod is worth used. Since the MX 2000P is considered a low-quality tripod, replacing the plate is generally not a worthwhile investment—especially for a heavier camera like a Canon 5D Mark III. In practical terms, you’d likely be better off putting that money toward a sturdier tripod or head with readily available plates.