Summer of 2007, I went on Carnival Victory's 5 day trip to Canada from New York. It was fun, though I thought it was too short. I went in the middle of August, there was a heat wave in New York, but I was cold in Canada.
There's a bunch of random things to do in both cities. Back in 1917, there was a big explosion in Halifax, I heard it was the largest man-made, non-nuclear explosion ever. There are artifacts on display from that. There's also stuff from the Titanic disaster, since many of the salvage ships back in 1912 sailed into Halifax.