PARIS — Centrist Emmanuel Macron and far-right populist Marine Le Pen advanced Sunday to a runoff in France’s presidential election, remaking the country’s political landscape and setting up a showdown over its participation in the European Union. French politicians on the left and right immediately urged voters to block Le Pen’s path to power in the May 7 runoff, saying her virulently nationalist anti-EU and anti-immigration politics would spell disaster for France. The absence in the runoff of candidates from either the mainstream left Socialists or the right-wing Republicans party — the two main political groups that have governed postwar France — also marked a seismic shift in French politics. Macron, a 39-year-old investment banker, made the runoff on the back of a grassroots campaign without the support of a major political party. With a wink at his cheering, flag-waving supporters who yelled “We will win!” in his election day headquarters in Paris, Macron promised to be a president “who protects, who transforms and builds” if elected.