I'm up there all the time (GF lives up there). CA side is where you want/need to stay American side is worthless except for Seneca Niagara Hotel.
If you plan to play Then Pick there or the Fallsvue Hotel both offer a P*ker rate. If not go to the Hilton or the Marriot. Get a Fallsview room in either.
When in Canada...
In any case when up there go to Niagara on the Lake. (rent car or take a tour) Its got a downtown area with candle shops, kitchen shops, and other things of the like. Also some nice resturants. Stop in the cigar shop get your self a cuban btw.
Go visit a Winery, Inniskillin is pretty close and makes some decent wine. The tour wasn't expensive and my GF loved it.
Linky
Do the Maid of the Mist your if its your first time there. It's touristy but cool.
American side, go to the top of the falls resturant and/or walk around the park.
If you have time and want to do a "guy" thing go to the anchor bar (in buffalo) which is like a 30 minute trip just to go see the home of the buffalo wing.