I'm not aware of any cajun workshops around here. The closest thing from here would be the Carrefour mondial de l'accordeon in Montmagny, Quebec, just about 1.5 hour east of Quebec City. For fiddlers, there's a big fiddle festival in Halifax which was last week, and there's a big annual workshop/festival event in Cape Breton, but it's very scotish style. Finally, I'm aware of another mostly fiddle oriented camp in Ontario every summer. I forgot the name of it.
Not a whole lot of cajun accordion.
Ciao.

If there is a performance venue in your area that puts on bluegrass, or Celtic, or "singer-songwriter" music, you could maybe arm twist somebody into hiring a Cajun band for a concert. Many of the folks who tour have also been teachers at Balfa or Augusta and are happy to give a lesson while in town.

S'b'B

You were wondering who was farther north--Halifax area, the capital of Nova Scotia, is around 44 degrees north latitude, so parts of Montana are farther north than we are, the Canada/US border being the 49th parallel. Montreal, Quebec is a little farther north than us. We're not freezing up here right now though--70-80F. temperatures.