I used to go to grad. school in Buffalo, NY which is just on the states side of the border. It has been awhile, so I'd be a bad person to ask for advice on lodging, cars, etc. But as for the attractions to see, I'm pretty sure most everything I'll mention is still around.
Make sure if you see the falls that you go on the Canadian side; the horseshoe shape is only apparent from that side (and they tend to do more like lighting it up at night). Near the falls (again on the Canadian side) is the botanical garden, which during the spring / summer is very beautiful. If you like to gamble, there is also Casino Niagara. In Buffalo, there is an aquarium. And you may want to stop at the Anchor Bar for lunch to experience the original "Buffalo" wings (although there are tons of wing-joints all over the city; some are even better than the Anchor's, but for historical purposes you may just want to go to the Anchor).
Toronto is also pretty close (I think about an hour or two north from Niagara), so you may consider a day trip up there too. Toronto offers a lot of big city attractions, like shopping and good dining areas. There is also a Medieval Times up there and in the late summer is the CNE -- the Canadian National Expo is like a gigantic state fair with many attractions to visit.
If you like sports, many national teams are in the area. Toronto has the Blue Jays (Baseball), the Raptors (Basketball), and the Maple Leafs (Hockey), while Buffalo has the Bills (Football) and Sabers (Hockey). Because of their closeness to each other, wherever there is a "border battle" between the hockey teams, there is a lot of excitement all over the place.
There are also all sorts of fairs and festivals in the area. If you're there in the early part of July, both countries have big national holidays which in that area tend to become one big week-long celebration: Canadian Day is celebrated July 1st and the US's Independence Day is on the 4th. There's also art expos in both Buffalo and Toronto, maple syrup is made in that region and tend to have festivals showcasing its production, and Toronto has a Renaissance Festival.