Rome is pretty easy to tour on your own. You will find many write ups and advice.
Florence is a pain in the ass to get to on your own. People do it, but, personally, I’d only go to Florence on a cruise stop if I had a burning desire to see Florence. Consider Lucca as an alternative.
Unfortunately, even Lucca is a bit tricky to get to via public transportation from the port. We rented a car which worked out great, but isn’t for everyone.