It would be very easy to do your own thing - the railway runs along the coast quite frequently.
The train from Cannes goes straight thru to Monaco and isnt expensive so no need to do organised tour. In Monaco there is a little street train that goes right round the town and has commentary on all the interesting sights and you can get off and on whenever you like.
Great train service all along this coast, easy to manage & cheap.
Our first cruise next June, and I was wondering the same thing. We have been told that the train service Cannes to Monte Carlo is good. Did you actually do your own thing when you went? If so any tips.