Aye, there's the rub.We know almost nothing of his actual military career.We have two sources, family lore, i.e., stories passed down by descendants of his sons.All say that he was a colonel - or high ranking officer - under Napoleon and that he was a topographical engineer.(We do know from C&O Canal records that he did work as an engineer for them.)
The second source are Masonic documents presented to him, the first in 1810 on board the prison hulk Kronpricen (a very sea worthy Danish ship which had been hulked and moored off Chatham) and the second in 1813 at Chatham.In both documents he is described as an "officier de commerce".It seems that could indicate a commission given on board a vessel in time of war - or not.
In both cases he is given as a native of Toulouse - which is, of course, the western terminus of the Canal du Midi.
Bottom line - I will have to locate his POW record before any military information.