"In this study, the Maine Department of Transportation is considering implementing either rail or Bus Rapid Transit service between Portland and destinations north of Portland. Bus service would be provided in the I-295 and I-95 corridors, and the following three rail corridors will be analyzed for potential funding... Portland to Yarmouth, Portland to Brunswick, and Portland to Auburn."
There is a wealth of information on the site, such as studies that have been completed, powerpoint presentations, and plenty of maps. I encourage you to spend some time looking around.
This map shows a couple of different options as far as rail service into Portland from the North. One option, using publicly owned land, would involve repairing the rail bridge that runs next to Tukey's bridge (which carries I-295) and would presumably have some impact on the Narrow Gauge Railroad attraction along the Eastern Prom. Another option would have trains coming in more from the northwest on rail that belongs to PanAm. Do note that the only currently existing train station in the map below is the Portland Transportation Center.
I don't have much to say about the project, except that I obviously support it and it sounds like they are on the right track (pun intended). While rail service (utilizing existing rails) would be my first choice, a bus rapid transit (BRT) system would have just as many benefits and would likely be easier to implement. I haven't read enough into it to determine how a rail service would work with the (eventual) extension of the Amtrak Downeaster to the north, but I'm sure that is somewhere in the notes. I would also be curious to know if there is any project like this for the southern side of Portland (currently served by a few shuttle buses and the Amtrak at Old Orchard Beach, Saco/Biddeford, and other points south).