There are references to the three Canadian ports in a cruise blog called Exploring the World from the Inside Cabin (https://www.theinsidecabin.com). They visited these locations during their 2022 Canada Greenland Iceland Cruise. Someone else posted from the same cruise with their information from the ports but I can't find the link right now.
we find that sometimes cruise tours cram too much into one day. You might want to look at renting a car or booking a taxi (book ahead) so you can go at your own speed.
From Halifax, Peggy's Cove is beautiful, as are some of the small towns nearby (Mahone Bay, Chester, Lunenburg). In Halifax, The Maritime Museum of the Atlantic (with the Titanic Exhibit and information on the Halifax Explosion in 1917) is also interesting. Depending on your time in port you could probably to both on your own.
From Sydney, the Alexander Graham Bell Museum is very interesting. You could easily spend a few hours there if you like that sort of thing. It is an hour drive (without stops from Sydney to Baddeck). There are also some other options close to your route to Baddeck, as well as some scenic areas both in Baddeck and on the route. The Fortress of Louisbourg is also interesting, but is in the other direction.