There is a bus www.acadianbus.com (902) 742-0440 that runs from Chester, NS on Route 3 at the Quik Way (275-5173) store (about a mile north of Tim Hortons') to both Halifax, NS and Yarmouth, NS. The bus stops at the store on the way to Halifax at 10:55 am, and arrives in Halifax at the bus station at 11:55 am. If you desire to go to Yarmouth, the bus stops at 7:25 pm, and arrives in Yarmouth at 11:55 pm. Should you be going to catch the ferry, it is recommended that you make reservations for accommodations in advance, due to the late arrival time. There are a number of motels, hotels and B&B's in Yarmouth. They vary in price quite a bit.
There is also a bus that runs between Halifax and Bangor, Maine. www.acadianbus.com (902) 742-0440. This bus departs Halifax at 7:15 am and takes 12 hours to get to Bangor, arriving at 6:10 pm. The price for a senior is $120 and there are two transfers. (I don't know where they are….) From Bangor to Halifax, the bus departs at 11:45 am and arrives in Halifax at 00:10 am.
There are a number of buses that go from Bangor to Boston daily. I believe the rate is $78 if you purchase the ticket seven days in advance. There are also buses that run between Portland and Boston, should you take the ferry. In 2005 I took the bus from Portland (Bus terminal is at 950 Congress Street) to Washington, DC. It cost $50. There were other buses about every two hours. They all (as I recall) go through Boston and New York. I stayed at a nearby motel that was moderately priced.
The train runs from Halifax to Montreal www.viarail.ca and takes 20 hours. The train leaves Halifax in the early afternoon. The train from Montreal leaves in the evening.
Amtrak has service between Montreal and Boston or New York.
Be advised that unless you really like trains this is a long and more expensive way to go, compared to air travel.
There are a number of airlines now that fly in and out of Halifax, and they change quite a bit. I would advise avoiding Air Canada, as they are usually the most expensive.
A ferry (The Cat) runs between Portland, Maine and Yarmouth on the weekends and between Bar Harbor, Maine and Yarmouth during the week (as of 2007.) If you have never taken a modern high speed ferry (50mph) this is an experience. Last I checked a car and one passenger to/from Bar Harbor was $500 round trip.
Another ferry runs between St. John, New Brunswick, and Digby, Nova Scotia. (888) 249 -7245. This ferry departs St. John at 12:15pm and 11:00 pm in the winter and at 0:45am, 9:00am and 4:45pm in the summer. It departs Digby at 8:00 am and 4:30 pm in the winter and at 5:00 am, 1:00 pm and 8:45 pm in the summer. It is about a four hour trip, and in 2007 cost for a car war $70, and a passenger was $17.50. Three things to note about this ferry. (1) There has been discussion about eliminating this ferry. (2) Once you get into Digby, you will have to find transportation to your final destination. I do not know if there is bus service, but I believe there is a similar bus to the one that runs from Halifax to Yarmouth along the south shore. I have been told that a bus goes to Digby also from Halifax to Yarmouth. I do not know times or if this bus is still running. There are a number of motels and B&B's in Digby.
Just in case you've heard about other ferries, there has been talk about ferry service between Nova Scotia and the Boston area. No such ferry has been put in service as of this time (early 2008). The Scotia Prince, which ran for years between Portland and Yarmouth, stopped running several years ago after a supposed dispute with the city of Portland, Maine.
Of course, no matter how you get to Chester, you will have to take a ferry to and from Big or Little Tancook Island from Chester, unless you have or know someone with, a boat. Basically the ferry runs four times a day except on the weekends, and on Friday there are two additional runs in the evening. On weekends and holidays there are only two runs. Check this website for the ferry schedule.