PA has a series of signed bike routes. I have looked at some of them and think they are nuts in places. Some scary, high-traffic roads. I think I understand why they did what they did--they want to use state-maintained roads, but that doesn't make it right.
Also, a while back all the links I had bookmarked stopped working and I have not bee able to find a link that takes you to the index that in turn allows you to see each route.
Here is a PDF of the route network:ftp://ftp.dot.state.pa.us/public/pdf/bikes/bicyclepa.pdf
Here is what I think is the easiest way to get the maps for each route:http://www.pahighways.com/other/bicyclepa.html
Click on the internal "maps" link for each route. That will produce an overview map of the route. Click on each circled number segment to see the individual segments. If you clink on the "directions" link, you will get a cue sheet of sorts.
Here are some suggestions with the disclaimer that I am not familiar with some of the roads/routes I am suggesting:
1. You could follow ACA's Atlantic Coast Route from Windsor Locks to Port Jervis, NY. From there, you can cross into PA at Matamoras and pick up the spur of PA Route Y, map segement 29B. Take that to main Route Y and follow that to Route G. Take Route G all the way down to Bedford. Using Google biking directions, get biking directions from Bedford to Cumberland, MD (It should give you three options.) Cumberland is the southern terminus of the Great Allegheny Passage rail-trail. That will take you very close to Pittsburgh. In fact, by sometime in June the last sesment into Pittshburgh is supposed to be completed.
2. Do 1 above but at Bedford, get on Route S west, gets onto the GAP trail at Rockwood (map section 9).
3. Take the ACA route all the way to Conshohocken, then take the Schuykill River Trail to PA Route S.
A couple of notes: I haven't been up there lately, but it's my understanding that natural gas fracking activity has increased truck traffic on the northern tier of PA, which is used by Route Y. The good news is that you leave U.S. 6 and jump on Route G at Ansonia.
Can't tell you much about Route G except that it uses a porton of the Pine Creek rail-trail, which is very nice, and that it passes through the heart of Pennsyltucky. Expect hills when not on the trail.
I am a big fan of the ACA route south of Port Jervis through Lambertville, especially the section through the Delaware Water Gap National Recreation Area. You then continue down the river on nearly all quiet roads in PA and NJ and can pick up a rail-trail between Frenchtown and Lambertville, NJ. The eastern part of Route S also takes you through the Conoestoga Valley, which is quintessential PA Dutch. However, I understand that option 3 suggested above is the long way around. I live in Philly and am hoping to ride the GAP/Route S home from PGH in mid-April.
Send me a PM if you have any questions or would like more info. There are slight modifcations I would make to the eastern part of Route S based on my riding experience.