Rue Saint-Denis is the long spine of French Montreal, and the Quartier Latin is where it's busiest: students, theatres, café terraces, and the bookshops that mark out whose city this is. Three kilometres up the street, best in the evening when the terraces fill and the marquees light.
Start at Berri-UQAM, the busiest interchange in the network, in the middle of the university quarter. Walk north up Saint-Denis through the theatre blocks — the Théâtre Saint-Denis and the cinemas around it, the French-language entertainment district. Above Sherbrooke the street opens into its terraces, café tables on the pavement and the long unhurried drink; take a seat with no plan and watch the street do the work. The bookshops are folded in among them, new and second-hand, the clearest sign of the language the city thinks in.
End at Carré Saint-Louis, the Victorian square of turreted, polychrome houses built for the French-Canadian bourgeoisie and lived in since by its poets and singers. Sit by the fountain. Sherbrooke is a short walk west — or keep going north into the Plateau, because the spine doesn't stop here.