Wow. The maker is Jean-Charles Cahier (1772-1849), successor to M-G Biennais, Napoleon's silversmith. Cahier, working from 1801, has some 86 items on France's register of historic church silver, including a font at the Malmaison Chapel and a bread offertory plate made for the 1825 coronation of Charles X, the last Bourbon King of France.
About which, the arms on your plate are
the royal Bourbon arms, of both Louis XVIII and Charles X. The date is right, the maker is right, and the arms are right, so you might have royal Restauration piece there from the last of the Bourbons. I say "might" because the arms were also technically the arms of all France, and it's far more likely to have belonged to some high-minded loyalist subject.
Either way, it's a fabulous piece of silver and French history; congratulations.
P.S. Great photos, by the way.