Beachgoing in Cannes has more to do with exhibitionism and voyeurism than with actual swimming.
Plage de la Croisette extends between the Vieux Port and the Port Canto. The beaches along this billion-dollar stretch of sand aren't private; in the strictest sense, they're payante, meaning you must pay from 15€ to 44€. You don't need to be a guest of the Noga Hilton, Martinez, InterContinental Carlton, or Majestic to use the beaches associated with those hotels, though if you are, you'll usually get a 50% discount. Each beach is separated from its neighbors by a wooden barricade that stops close to the sea, making it easy for you to stroll from one to another.
Why should you pay a fee at all? Well, it includes a full day's use of a mattress, a chaise longue (the seafront isn't sandy or even soft, covered as it is with pebbles and dark-gray shingles), and a parasol, as well as easy access to freshwater showers and kiosks selling beverages. There are also outdoor restaurants where no one minds if you appear in your swimsuit.
For nostalgia's sake, our favorite beach is the one associated with the InterContinental Carlton -- it was the first beach we went to, as teenagers, in Cannes. The merits of each of the 20 or so beaches vary daily, depending on the crowd. And since every beach allows topless bathing (keep your bottom covered), you're likely to find the same forms of décolletage along the entire strip.
Looking for a free public beach where you'll have to survive without rentable chaises or parasols? Head for Plage du Midi, sometimes called Midi Plage, just west of the Vieux Port (tel. 04-93-39-92-74), or Plage Gazagnaire, just east of the Port Canto (no phone). Here you'll find greater numbers of families with children and lots of caravan-type vehicles parked nearby.