Brunswick ME is the end of the line for the Downeaster, so the original poster's worry about have to hoof it to get his bike off shouldn't be an issue. They won't reverse the train or pull it off to a storage track while there are still passengers aboard, so if you have to fuss with your bike to get it off the rack or drag it the length of the car because they only opened the door at the far end, they will see you and won't move until you are off. It probably won't be crowded, so it should only take much less than a minute to walk your bike to the far end of the car. If it is heavily loaded, every will be getting off, so you just need to wait at the end of the line.
If there is a special separate bike storage area, the conductor will probably load and unload it for you. They generally don't let passengers into the baggage cars. I'm not sure about the baggage areas of cabbage (combination coach and baggage) or other special cars.
It's not like trying to get a bike off a packed commuter train where lots of people are getting on and off and you only have a few seconds to fight your way through a crowd! You'll be fine.
