You could probably use Google Maps to plan out your route. Your biggest challenge finding a route and avoiding highways will be crossing the Susquehanna River. Unless you go about 25 miles out of the way through Holtwood, PA, you’re stuck with Route 1, Highway 40, I-95, or a long swim to cross the river.

However, if you are willing to spend a couple of days to make the trip, it could be an enjoyable ride on the back-roads of northern Maryland and Southern PA. It’s quite beautiful country. Just beware of a fair amount of backwards people, complete with an abundance of rebel flags flying from houses along the roads.

Check out the bike coalition of greater Philly. Brandywine area is gorgeous. All the bicycle coalitions (Mass, LA, etc) are user-friendly and have good contacts.

http://www.bicyclecoalition.org/

And this forum: http://www.bikecoalition.com/

Biller’s Bikes in Havre de Grace, MD offers cycling group bridge crossing services over the Susquehanna River via the Hatem Bridge. The service currently operates March through November and generally requires a 48-hour advance reservation. Bridge service includes a host of trail comforts. See www.billersbikes.com for information.