I love Halifax. You can walk the seawall and see so much. Right where the ships dock is the immigration museum and I found my grandmother's ship in a picture posted in there. Of course there are lots of touristy things along the waterfront but there is also some fantastic art and some great historical spots. The HOHO will also take you to some great historical places but you don't have to do it that way. Halifax is very hilly apart from the sea walk, though, so the HOHO helps.
The beavertails are a lot like bannock but not as fluffy and they are worth having just to say you did. There is also a stand on the board walk that sells everything bacon. There are tons of great restaurants in Halifax too. A bit of a Maritime foody centre. If you do wander the sea walk, there is a vessel there that not only survived World War I but the Halifax Explosion AND World War II. It's rusting out so you may want to take the opportunity to see it now. Personally, I'm going to Peggy's Cove and Lunenberg. Being from the West Coast of BC, it's not that exciting to me but my sister really wants to see Peggy's Cove. I've been to Halifax a couple of times and know I will take every chance to go again, so I can sacrifice one trip! In the defence of the places though, it's a great lighthouse, a marvellously dangerous aspect and a lovely town/village at Peggy's Cove and a beautiful town in Lunenberg. You really can't go wrong no matter what you pick