It is difficult to gauge with these photos. He would have had to take some measures. Since the diameter of the mouth, or barrel length, etc.
But at first seen, it is indeed a French bronze cannon, used in the seventeenth century.
Here are the French seventeenth calibres:
4-pdr, 6-pdr, 8-pdr, 12-pdr, 18-pdr, 24-and 36-pdr pdr.