After just going earlier this year, I can say the view of the falls from the Canadian side is better, but I like the "park" aspect of the US side. On the US side its much more like a national park. On the Canadian side, its much more touristy imo.
If you want to do "maid of the mist" that is the US side. The Canadian side has one as well, but I think its named different (not that it matters lol). I really think our best viewing was while walking across the rainbow bridge into Canada (aside from maid of the mist).
We really liked 4 mile creek campground as well. Its close enough to the falls to not be a burden to get there, right on lake ontario if that matters, had one of the best cleanest campground restrooms/showers that I have been in (again probably doesn't matter when you have a class A). People were nice, and your park pass there can be used at any of the parks on the US side as well. I really didn't see much checking or inspection of those, but maybe they did it when we were out and about.
We drove through Canada at Sarnia, but we live within an hour of there so it didn't make sense to do it any other way. Don't forget the passports! We had no problems getting in through Sarnia or across to NY, but on the way back through Sarnia they boarded the TT to take a peek. Right at the gate though, we didn't have to pull over for inspection.
If you stay at 4 mile creek, Fort Niagara is right nearby. You may or may not have time to visit that, though we ran through there ourselves and found it pretty neat. Pretty much literally ran through (we didn't have much time but wanted to see it, so did the whirlwind tour style lol).
On the Canadian side you can do the walk under the falls tour which is neat. They have a similar one on the US side but we didn't do that. We did climb the stairs up the falls edge there...crows nest I think it might have been called? As well as the observation deck which also was pretty cool.
Oh, if you walk the bridge to the Canadian side and want to walk to the falls you can...but its a long walk, bring good shoes. :)
