Complex sentence: Massé had previously been a candidate for the Bloc Populaire Canadien in Cartier 1943 (when he lost by only 100 votes) and 1945 and would later, in the 1963 Canadian election be a candidate in the riding of Laurier for the New Democratic Party.
Split into simpler sentences: Massé had previously been a candidate for the "Bloc Populaire Canadien" in Cartier 1943 (when he lost by only 100 votes) and 1945. In the 1963 general election, he stood as a candidate in the riding of Laurier for the New Democratic Party.