Specific electric power doesn't go anywhere. Electricity is a voltage potential difference between sources and end users and flows through a grid. This is why you can't just buy, say, wind or solar power.
Both Huntley and the NYPA Niagara Falls hydro plant send power into the grid. You can't distinguish what power comes from where. Because Niagara Falls generates more power than Huntley, I would say that almost certainly this big solar panel factory will be powered principally with power generated by hydro.
That said, you can charge people different rates. NYPA, as a NY State Authority (thanks Robert Moses for creating monsters like this), can cut deals with downstate users for cheaper power. However, a certain amount of power has to be distributed at low cost prices to Western New York businesses. This is part of the NYPA licensing process. It is commonly referred to as low cost hydropower, but again, a voltage potential is a voltage potential - it doesn't matter to the grid who generated the potential.
I did get a chuckle reading the Buffalo News this morning (yes, I devour the dead trees version every day - it's a great paper) that they are expanding this previously announced solar plant due to the availability of a low cost power allocation from NYPA. Irony indeed.
Still, as Obama says, you have to pursue "all of the above" so I am glad they are ramping up production.