Strasbourg and Cannes are both French, but that is nearly where the similarity ends. Strasbourg is a half-timbered Franco-German cathedral city on the Rhine; Cannes is a Mediterranean film-festival resort on the Riviera. Comparing them mostly reveals what kind of trip you actually want.
Strasbourg's Old Town Around the Cathedral centers on the towering Strasbourg Cathedral (Cathédrale Notre-Dame), with its Cathedral Astronomical Clock Demonstration drawing crowds each hour. Cannes centers instead on Boulevard de la Croisette and the Croisette District, backed by the glossy modern Palais des Festivals et des Congrès. One is Gothic stone; the other is Riviera glass and red carpet.
Strasbourg rewards wandering the canals of Petite France District and Petite France (Medieval Quarter), crossing the Covered Bridges (Ponts Couverts), and passing through Place Kléber to the Palais Rohan (Rohan Palace). Cannes has one comparable pocket of history in Le Suquet (Old Town), overlooking the harbor, with the Croisette Tower (Tower of Siracusa) marking the shoreline nearby.
History fills Strasbourg's Musée de l'Œuvre Notre-Dame (Notre-Dame Museum) with centuries of cathedral sculpture. Cannes leans lighter: Musée de la Castre is its main museum, while Old Town Guided Walking Tours and the Lérins Islands Ferry Excursion pull visitors toward the water instead of galleries. Strasbourg is a city for indoor afternoons; Cannes is not.
Strasbourg's obvious day trip is Colmar (35 km), Alsace's storybook wine town. Cannes offers two: Antibes for its old port and ramparts, and Grasse (Perfume Capital) for its perfumeries. Either way, you're choosing between half-timbered villages and Riviera towns built on scent and yachts.
Choose Strasbourg for Gothic architecture, a walkable medieval old town, and an easy trip to Colmar (35 km). Choose Cannes for Riviera beaches, the Croisette, and day trips to Antibes and Grasse (Perfume Capital). Strasbourg suits history lovers; Cannes suits sun-seekers.