You would have to take a bus from DTD to the Boardwalk. If the bus goes to Swan/Dolphin/Yacht/Beach first, then the Boardwalk would be next. Maybe 45 minutes? If you are going from Boardwalk to DTD, it would be about 20 minutes to the Marketplace from the Boardwalk. Another 5 to Westside.
Plus if you are going during the day, it will probably also stop at Typhoon Lagoon after DTD and before the Epcot resorts.
No direct waterway, so no boat.