It appears that LCB Brasserie Rachou, the former La Cote Basque, in NYC has both choucroute garni and cassoulet on its menu. La Cote Basque was my favourite restaurant in NYC and I am glad to hear it has re-opened in a new less formal style and is in very fine form.
While this does not help the OP to find the above items in Montreal, NYC is only a 1hr 15 minute flight!!