The main NS trunk going north from Harrisburg now is the line that they just acquired from CP. It runs through Sunbury, Wilkes-Barre, Scranton onto Binghamton and then along the Susquehanna valley through Oneonta to Schenectady. Historically this is a combination of PRR, Lackawanna (Delaware, Lackawanna and Western which became part of Erie-Lackawanna), and Delaware and Hudson (DH) routes. There is also the other leg of the (ex-Erie) Southern Tier Line connecting from Binghamton to Buffalo. And there is the NYSW from Binghamton to Syracuse (ex DLW) and Utica (ex DLW) too, but they appear to be secondary in nature at present.
The Harrisburg to Schenectady via Binghamton is part of the NAFTA Corridor which connects at Schenectady with CP to Montreal. And Oh yes, it runs over the famous 100 year old spectacular Tunkhannock Viaduct at Nicholson PA. If and when the (ex-DL&W) Lackawanna Cutoff gets completed in NJ and passenger service is restored from New York to Scranton, then the next step would be to extend service to Binghamton from Scranton. In a study for restoring passenger service to Binghamton both PA and NY have shown a preference for this route rather than the old southern Tier Erie route via Port Jervis (which has passenger service upto Port Jervis provided by NJT under contract from MNRR as part of MNRR west of Hudson service). This choice is due to projected running times. The old Lackawanna route via Scranton is faster by a couple of hours than the old Erie route.Both the old Erie route and the old D&LW route are quite scenic, with the Erie route having a certain edge in my opinion, as it winds along the Delaware River valley, which also makes it the slower route.
The old PRR trunk from Harrisburg through Sunbury, Williamsport, Olean to Buffalo is still an active NS freight route, but with very low chance of getting any passenger service. Also, currently there are no plans for passenger service between Harrisburg and Scranton along the NAFTA Corridor.