I used 12-pound as an example because I knew for a fact it existed, but the question obviously applies to all sizes of cannons. I understand that cannons were referred to by the weight of their ordinance, i.e., how many pounds the cannonball weighed. But, after the French Revolution, did they change the name of these weapons to match the Metric system, or did they continue to use pounds?
The French referred to it as the Canon obusier de 12 - because the calibre was 12cm. They also used the Canon de 12 and Canon de 8, which were 12 and 8cm calibre respectively.
They adopted these systems in the 1840s to 1850s, and used punds until then.