Clifton Hill is such a fun touristy place!! I used to love going there a lot when I feel like being five again, and all they asked at the border was, "where were you born? Okay, go ahead." lol
Casinos are fun, Buffalo had a new one put up a few years ago, and while you're there, check out the CCO!
The falls are really beautiful at night because they light them up, and sometimes they do special colors for special events!
The Butterfly Conservatory is kind of interesting because (well, IMO it is!) the butterflies are so beautiful and we never really get them in Buffalo.
There is also Niagara on the Lake (US, IIRC), though I've never done it, it supposed to be great, plus there are wineries there.
Though, overall, the Canadian side is much nicer. If the border wasn't so much of a hassel now, we would be going there so much more often!
Hope you have a good trip and anniversary!!