I've seen several lists of LA/Tex Cajun box builders and have met a few personally, but I've never seen a similar list of Quebecois builders. Who are the leading French/Canadian builders?

Hi John,
There is a list in the materials that came with Denis Pépin's video, but it was not a complete list. There are "major builders" (25-35 instruments per year) and then there are some builders who build fewer instruments per year, some of which are really unknown outside of Quebec. There are also some instruments floating around that were made by people who only ever made 1/2 dozen or fewer boxes.

The two "major" builders (I put the quotation marks around "major" because by accordion industry standards, they are still small operations) are located in Montmagny:
1. Messervier: the oldest builder in Quebec, Marcel and his son Marcel. Superb instruments.
2. Mélodie: Raynald Ouellet and Sylvain Vézina (Marcel Messervier's nephew).
I can highly recommend both of the above makers!!! (And I personally play a Mélodie.)

Small builders:
1. Réjean Simard
2. Desgagnes
3. Clement Breton (took some time off from building until retirement)
4. Boutet
5. A few others -- names I've forgotten.

Of the current small builders, I recommend Simard and Breton, although I cannot say for certain whether Clement Breton is currently making any boxes. The ones that I have tried were excellent.
Over the years, the trend in "the" sound has changed quite a bit. The boxes from the seventies were unbelievably loud, with no moveable stoppers; the recent trend includes tunings that are not quite as wet and boxes with four usable stops. This is my observation from hearing dozens of players in live settings and sessions, not necessarily recorded players. By far, "the" box for serious amateur players and some of the "pros" has been Messervier. You'll see Mélodies, too, but they haven't been made for very long so there are certainly fewer floating about. I went to one event where several dozen players played, one after the next, and everyone had a Messervier except for Réjean Simard and one or two others.
Now I've written too much.
-Andy

Thanks so much. Obviously there are not as many Quebecois builders and they seem to make fewer boxes. I expect this is why the quality of workmanship is higher.

Among other reasons

Hi this site is the annual accordion festival in MONtmagny quebechttp://accordeon.montmagny.com/carrefour/index
Foe builders there are more than these , but I know of
Marcel Messervier in Montmagny,
Reynald Ouelette (Mélodie), also of Montmagny and
Marcel Desgagné makes Sagné accordionms from up in the
SaguenayChicoutimi area

Where do you live Andy?

Hi Maz,
I live in northern Vermont, not far! Where are you?
-Andy

Halifax, Nova Scotia. Cheers..:-)