No, you can book a through trip from BAL to Portland via Amtrak.com or an agent. When your tickets print you'll get what's called a place holder ticket. It's a useless ticket not good for any form of travel, but printed on the ticket are suggestions on how to get yourself from North Station to one of the two southern stations. It's because of this place holder ticket that ARROW can handle selling you a through trip as it were.
Is it a guaranteed connection from the NE regional to the downeaster? Just curious.
I thought anything the website would give you in one single-trip booking was a guaranteed connection.
Connecting Trains
Amtrak does not normally guarantee connections of less than 60 minutes (90 minutes between arriving long-distance trains and local trains in the Northeast Corridor). Please call Amtrak 1-800-USA-RAIL (1-800-872-7245) or your travel agent if your planned itinerary includes a shorter connection. A guaranteed connection does not ensure that such a connection will always be made. In the case of a missed guaranteed connection, Amtrak will provide alternate transportation on Amtrak, another carrier, or overnight hotel accommodations, at Amtrak's discretion. (from Amtrak's website, go
here. )