Nature For The Blind has a directory of Braille trails for almost every state in the US and for many other countries.

Delaware & LeHigh National Heritage Corridor
From Wikipedia:   “The D&L Trail is a 165-mile (266 km) multi-use trail. The trail incorporates rail trails, rails with trails, share-the-road sections, and canal towpaths…The trail follows the route that anthracite coal took from mine to market. It winds through northern mountains and along the banks of the Lehigh and Delaware Rivers through northeast Pennsylvania, the Lehigh Valley, and Bucks County. The D&L Trail passes through towns, industrial powerhouses, and along remnants of the Lehigh and Delaware canals. This earthen path exposes walkers, hikers, bicyclists, and others to Pennsylvania wildflowers, waterfalls, and wildlife.”   The corridor crosses may state, county and local parks.
Here is their website.     Map
Lehigh Canal North  from TrailLinks
Lehigh Canal South from TrailLinks
Walnutport to Weissport from TrailLinks

ExplorePAtrails.com is a searchable site  where you can put in your parameters such as hiking, length and distance from a city or zip code and it will come up with a list with links to information about trails.  For example, I chose within 100 miles of Allenstown, any length, hiking, and wheelchair and it turned up 72 ADA trails!

American Trails has links to information about many trails in Pennsylvania.

believe@Magee from the Magee Rehabilitation Hospital has this great page with information on wheelchair accessible trails..

The Rails-to-Trails Conservancy lists wheelchair accessible trails in Pennsylvania.