Can anyone recommend a small group tour company to take us on a day trip to Canne, Nice, Grasse and surrounding areas since we will be docking in the port of Cannes on a Mediterranean cruise for the day?
I didn't take any tours in that area but want to point out that the regional trains run frequently along the coast between Cannes and Nice, so if necessary you can do it on your own. There are both trains and buses running between Cannes and Grasse. Travel time is about half an hour. That's a different rail line from the one running along the coast.
In addition to any replies you get here, look at Cruise Critic's France Ports Forum: https://boards.cruisecritic.com/forumdisplay.php?f=593
From Cannes to Nice, trains run twice an hour and are cheap. So, if you just want to see these two, it's easy to do on your own. Just go to Nice first thing, spend time there, and take a train back to Cannes and spend your remaining time before your sailing there (Cannes doesn't take long to see). But the logistics of seeing Grasse, Nice, and Cannes, all in a single day and without missing your sailing, mean that a tour will probably work better if you want to do all three.
If you are interested in self-touring, at Cannes or any of your other cruise ports, get Rick Steves Mediterranean Cruise Ports: https://store.ricksteves.com/shop/p/mediterranean-cruise-ports. This has all the details of what's involved in seeing each port on your own, so you can decide if you want to do that, book a ship's tour, or book a private tour.