In general you should have no issues finding gas but the Pilot, Love's, etc, kind of places are few and far between. We go every year from Waterdown to Carlisle, PA. When I still had my gas truck we would fill at Williamsport which was about the maximum I would push it on one tank. That was about 430 km. for me.
Just our personal preference but to vary the trip but we prefer to go I-90 to Batavia, then we take 63 & 36 down to Mt Morris from there where we pick up I-390. We also stay on 15 from Williamsport to Sunbury instead of I-180 just for the variation. We also found that in general gas in Pennsylvania was less expensive than in New York.