These were iron cannon (not bronze), inherited by the French from the Venetians in Preveza, Greece, in 1798. There is no date for the guns but I would expect that it was rather old, since the condition of the artillery parks in the Ionian isles (in Corfu and the mainland territories) was extremely poor when France gained the ex-Venetian territories. For example, many of the cannon in Corfu's citadel (the strongest position in the region) were not mounted, only lying on the ground when Gentilli and the expeditionary forces first landed.
The guns I am interested in were mounted on old, worn out wheeled gun carriages ("montées sur affûts à roulettes vermoulues de vétusté"). Does "affûts à roulettes" imply that these were garrison guns and not field artillery?
I am not sure of the nationality of the carriages but they were probably imported by the Venetians, which makes me think these 3-lbrs were not mountain guns (guessing that the Venetians were not campaigning in the mountains very often).
Note that the following response from Steven indicates these 3-lbrs may have really been Venetian 4-lbrs.
In any event, approximate dimensions for the cannon and carriage would be welcome.