I suggest you take the Pennsy( Biz Class is worth the Upgrade) during the Week, not Weekends, and go before May, from Pittsburgh to New York, spend the Night( Google up Deals on Hotels) since a Same day Trip from Pittsburgh to Portland isnt practical/ possible,and then catch the earliest Regional or Acela you feel comfortable with ( just get the Best Fare in Coach or Biz Class on the Acela) to Boston,( Back Bay or South Station).
Then Self transfer to North Station ( T or Ride Share/Cab)and take the Downeaster ( Biz,Class is nice on this Train but Coach is OK) to Portland,Maine.
Hotels ( and Seafood, but its Delicious)) can be Very Pricey in the Summer, especially on Weekends,and it can get Very Crowded in what is a Small Fishing Village.
I've stayed @ a Nice Days Inn that included Breakfast for $120(in Early May) a night and used Ride Share to/from the Waterfront.( In nice weather it's Walkable)
Keep in mind the Intermodel Station ( Amtrak/Bus Station) requires a Cab or Ride Share since it's located away from town.
Boston has excellent Seafood also, butHotels tend to be Very Expensive, even Higher than New York!