By the top floor, they're probably referring to the Skylon Tower. Really nice restaurant at the top of the tower. It rotates, so during your dinner, you get a 360 degree view of the falls and surrounding landscape. On a clear day you can see for many miles. I can't remember if you can make phone reservations, but you'll want to get your reservations for dinner early. If you get a dinner, you can also go to the observation deck. (else pay to go up there.)
I'm not sure that I'd call it "romantic" because my idea of a romantic dinner is after dark by candlelight.
edit:
If you can't tell from the picture on the first page of this link, it is the BEST view of Niagara Falls.
Skylon Tower
There are two levels of dining; I don't think the buffet qualifies as romantic by most people's definition.
dining
Apparently, you can make your reservations online. We used to just make our reservations early in the day, then show up at the proper time for our shuttle/elevator to the top.
another edit: Rather on the expensive side - you're paying for the view. It would probably be most romantic toward dusk - so that by the end of your dinner it's dark and the falls is all lit up.
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