Have you considered the Eastern Shore?
You would miss Baltimore and Washington entirely and have beautiful countryside.
Maryland puts out a cycling map - online and paper.http://www.mdot.maryland.gov/Office_of_Planning_and_Capital_Programming/Bicycle/Bicycle_Maps.html
From Crisfield you can take a passenger ferry to either Smith island or Tangier Island -
Then connect to another passenger ferry to the Northern Neck of Virginia.
Staying overnight at one of the island guest houses would be like dessert.
Then you could ride the Northern Neck to Fredericksburg.
From Fredericksburg you can catch Amtrak back to NYC and Upstate.
If you decide to do the Eastern Shore, you should be on the east side of the Susq -
Before you reach Maryland since there only one legal bridge in MD - and it's yucky.
You want to avoid US 301 - even avoid Hwy 213 when possible -
But you do have to used Hwy 213 to cross some inlets and rivers.
The biggest challenge is crossing the Delaware & Chesapeake Canal.
Personally, I'd catch a ride either on the bridge -
Or from the dock on the north side to the dock on the south side.
(Boaters have helped me out many times crossing water bodies.)
If you are willing to hitch across water -
Then heading down Elks Neck to Rogue's Harbor is a possibility.
Although the Eastern Shore is busier than it used to be -
It is still a lovely place - far removed from the urban scene.
(Holiday weekends can be crazy, however.)