Thank you for your review, VACATIONER, and to everyone else for the comments that followed. I even learned some, and I live here! BTW, the Union Oyster House is one of few places popular with tourists that is also frequented by locals. (Another is the Duck Tour.)
I imagine that Peggy's Cove and the main Titanic graveyard was a lot for one day. Some other options for future Halifax trips are the Maritime Museum of the Atlantic (that some of you mentioned -- they have a lot of Titanic stuff along with great historical information on Halifax Harbor) and the Pier 21 Immigration Museum. Both of these can be done on your own as they are close to the pier. (In fact, Pier 21 Museum is at the pier.) The Citadel is also fabulous, yet somewhat of a hike... worth it in the end, though. Halifax is one of those cities that requires numerous visits. We've been there five times, I believe, and we're still not done. Great tip on the traffic, btw.