BeforeYouGo.com

In Cannes the cruise ships anchor a little off the coast and you take small boats into the port.  When you exit the port you are in a pretty convenient location for walking around Cannes and can easily see several sights including the location of the film festival and a small outdoor market, as well as a beach.  All of that is within a fairly easy walk.  

From where the cruise tender drops you off, you'll walk to the right along the water to get to the Cannes Film Festival location.

From where you are dropped off you should be able to see a castle (pictured below on the right) that is up a hill and to the left.  It's a fairly short walk.  From that castle is where the picture at the bottom left was taken, which shows a harbor and the location of the Cannes Film Festival.

Getting to the other nearby cities in the area will all take a drive and I am not aware of any good public transportation options between the cities.