I would absolutely plan at least 2 days for the Trail from Halifax, if you can. It takes a full day from start to finish to minimally appreciate it. If you start from Halifax you could get part of it in, then do the rest the next day.
Personal recommendations: walk the Skyline Trail, between Cheticamp and Pleasant Bay. Easy hike, awesome views, and a good shot at seeing moose, whales & bald eagles. Cheticamp has the best restaurants (unless you have fancy/expensive tastes, then there are other places, but I couldn't tell you anything about them). Off the Cabot Trail, the road north to Bay St. Lawrence and further on to Meat Cove is great - camping in Meat Cove, at the top of a cliff, is well worth it as long as the weather forecast is good (we had to run to our car in the middle of the night to escape the wind and rain, only to see the tent then start to fly away). The Red Shoe pub in Mabou has good food and music. And if you're there on a Thursday night, definitely, definitely go the dance at Glencoe Hall, even if you don't want to dance.