Delaware Canal towpath in PA to New Hope, back on Delaware Raritan Canal towpath in NJ. Gravel surfaces great for hybrids and mtn bikes, suitable for road bikes, but I think you would want to have at least 20 mm tires.
Trains from NYC Penn Station run hourly, riding time 90 minutes each way. 2 bikes can be carried on either end of the double decker train cars, flipping seats up. You can secure your bikes with thin rope, sitting on seats across the aisle. Train begins at NYC Penn and ends at Trenton so you will not be rushed on and off. NJ Transit does not require a bike permit; one less hassle!
Online NJ Transit schedule: http://www.njtransit.com/sf/sf_servlet.srv?hdnPageAction=TrainTo
Note that NJ Transit senior ticket discount starts at age 62. Bring ID.
The 2 streets you take in Trenton are safe other than motor traffic. You will pass the State Capitol Building and other historical sites in Trenton.
This is an easy, most unusual ride for NYCC riders. But your speed will be slower than comparable distance on roads due to surface resistance of gravel paths. Except for access to the towpaths, you will only deal with motor traffic when roads cross the paths.
Caution is needed when passing under bridges while cycling north on the Delaware Canal towpaths. Be sure to gauge headroom as these vary. Also, there are a few blind spots as you approach these underpasses. You might need to walk your bike if you cannot duck low enough on a few underpasses. Or you can cycle to the right and cross the road that goes over the bridge. Be wary and respectful of oncoming path users.
Optional bathroom stop and Cumberland Farms on way north noted on cue sheet.
You will have no problem finding dining in New Hope or Lambertville. Advise bringing bike locks.