Ive done quite a few paths and trails using NJT or Metro North or LIRR though Long Island should only be done in the warmer months.

You can ride the Delaware and Raritan Canal trail from New Brunswick to Hamilton,NJ , its about 40 miles , i've walked 15 miles it between Hamilton to Princeton. Its relatively quiet not too many people.

They recently completed a heritage route south of Bordentown. So you could ride the Delaware & Raritan Canal trail from near the Cass Street RiverLINE station in Trenton , you access it via the Riverfront Park and Lamberton Rd and that will bring you to Bordentown which is about 8 miles. The Heritage route will bring you down Roebling and you can bike via the Back roads to Burlington which is about 9 miles.

On the NY side you have the Aqueduct pathway which runs from Yonkers to Irvington with a small detour in Tarrytown and North of Downtown Tarrytown to Scarborough and a small detour in Ossining and then from Ossining to the Croton Harmon Station or the Croton Dam. The Best Access is from Greystone Metro North Station. In Tarrytown you can alternatively ride along the Riverfront into Sleepy Hollow and access the trail from Gory Brook Rd entrance.