Cornwall - 2nd try
I don't know Cornwall at all but if you don't mind a drive there is a good pizza place in Mountain Ontario, called "Mountain Station Pizza". Here's a blurb that gives address and phone:
They only take cash and their hours may vary, so call ahead.
It's 80 km from Cornwall, so not right around the corner (perhaps too far for dinner), but it's one option.
I know there's a decent bakery in Maxville, Ontario (which is closer) but I'm not sure about restaurants.
Maybe ask in the New York board if there's anything decent in any of the cities across the border, like Massena.