In my opinion (and in the opinion of every person I've ever talked to who has visited Niagara), the Canadian side is much better. There seems to be so many more things to do and I like the view better. We stayed at Embassy Suites Falls View and we loved it!
Make sure to see the Imax film of Niagara, it's very interesting.
There are casinos there if you like that sort of thing, one is huge and fairly new. We don't care for casinos that much, but stopped in to get our money changed over and it was impressive.
The Clifton Hill area is a street where a lot of tourist attractions and shops are concentrated, such as Ripley's Believe it or Not. It is very bright and glitzy, so if that doesn't interest you, steer clear of that area. We only visited it one evening toward the end of our vacation.
Maid of the Mist is a must-see, it is an open top boat which takes you right to the base of the falls. You will almost certainly get wet, so be careful! They give you ponchos, but depending where you stand, the mist can really get to you!
A very short ride by shuttle bus from the heart of Niagara Falls is the Butterfly Conservatory, a giant tropical room filled with lush vegetation and literally thousands of butterflies fluttering around. They are everywhere, and many times land right on you! There is a pathway to follow around at your leisure. There are so many different kinds of butterflies. This was such a cool experience, next to the falls, it was the highlight of our trip; a very family-friendly activity.
There is a cable car ride that goes high overtop a giant whirlpool. We didn't get a chance to do this, though.
There is a boardwalk that goes along the rapids downstream from the falls. It is an easy walk, and a very different perspective than the typical view of the falls. It is neat to be right next to the rapids, they are SO powerful.
I was 5 months pregnant when we took our trip so I couldn't go on it, but the Whirlpool Jet Boat Tours sounded like SO much fun! It is definitely adventurous, the boats goes about 60 mph (I think) right into the rapids. I included a link for you to check it out.
We had dinner at the very top of Skylon Tower in a revolving restaurant. It overlooked the falls and was really cool. It is a little pricey, so go for lunch to get the same view at a cheaper price!
There is more stuff I could share, but this is already so long. Just pm me with any questions!!
http://www.niagarafallstourism.com/
http://www.infoniagara.com/
http://www.city.niagarafalls.on.ca/
http://www.whirlpooljet.com/
Laura