This paper deals with the treatment of expressions used in two French-speaking regions, Canada and France. According to the editorial policy of the Bilingual Canadian Dictionary, all usages particular to Canada must be marked in this work. But there are often very subtle differences in fixed expressions and collocations from one region to another. For example, there are only slight morphological or synctactic differences in the following expressions: tirer les cartes/tirer aux cartes, mettre les pieds dans le plat/se mettre les pieds dans les plats et faire le beau/faire la belle. In addition, there are expressions, which are of even more interest to us, that are identical in form but not in the way they are used, expressions such as avoir l’air fin et passer au travers. It is certainly not easy for Canadian lexicographers to determine the specific Canadian usage of such expressions. The only way to do so is to study these expressions in context, i.e., to analyze a representative corpus from each region. This paper presents the stages that Canadian lexicographers must go through if they are to distinguish the usages particular to a given community and to mark these differences in a dictionary.