Yep, as you exit the gates at MGM head to your left. You'll see a canal and the boat dock is down there.
The International Gateway at Epcot branches off from the World Showcase between England and France on the England side of the bridge.
We've never taken the boat all the way from MGM to Epcot or vice versa but most people say you can walk the route faster if you are so inclined. The boat is not very fast and as noted by dudspizza it goes to the Epcot resorts in between. The order is MGM>Swan/Dolphin>YC/BC/>BW>Epcot.