Given the amount of time you spend in Montreal, cross Banane off as there is a lot in Montreal in a similar style (though Banane is very good). Isabel and Quetzal are very different, but my preference runs to the Isabel cooking and wine list (Quetzal is new world only). The room at Quetzal is pretty special.
So Isabel, unless you have a preference for Mexican cooking over Spanish, in which case Quetzal. In either case, do stop by Raval (a short walk to either and same owners) for a drink and tapas before the meal (or after, if you can get in). Same architect/designer as Quetzal as well.