There are multiple bridges in the Niagra Falls area. Sometimes the waits can get into the two plus hour range. I generally use the Lewiston-Queenstown bridge. It is served by freeway at both ends and is the easiest crossing when traffic is light
. If traffic is heavy, however, I have waited up to 2.5 hours in bumper to bumper lines waiting to get into the US from Canada. I now have a Garmin that gives road conditions and have found the bridge advisories that they give to be very helpful.
Believe it or not, the Rainbow bridge, which connects the two tourist areas of Niagra Falls Canada with Niagra Falls US is MUCH faster in heavy traffic times, at least in my experiences. There is no commercial truck traffic allowed, plus they keep this bridge well staffed because neither side wants to impede the tourists going back and forth any more than necessary. Plus, if you do have to wait, you have a fantastic view of the falls to keep you entertained. The drawback is that both sides of the bridge put you onto city streets, in big tourist areas. They are fairly well marked, however, and not terrible to navigate. Both sides quickly get you back onto multi-lane, divided highways.
The Whirlpool bridge is also available if you are a Nexus subscriber - I've never used it.
A bit further south is the Peace bridge into Buffalo. I've used this a few times, but generally stick to the Lewiston unless traffic is bad.
If you have a smart phone, this link will give you current traffic conditions:
Generally crossings are pleasant, without any undue hassle. Be courteous, even if you are irritated, and virtually every agent I've encountered has been courteous in return.
Sometimes they are downright friendly and talkative about life in general, you know, almost like regular people. :-)
Just wanted to add:
I've visited both the US and the Canadian sides. I found the US side much more relaxing, plus you can visit the State Park above the falls - well worth the time. You can get right to the edge of the river, even wade in the river within sight of the top of the falls, a very interesting perspective. Granted, the Canadian side has the more spectacular views o the falls.
Also the Maid of the Mist tours are well worth the price, gives yet another perspective. The walk down to the river below the falls on the US side is also fun - gotta wear rain gear because you get right up to the falls and can reach out and touch them.
Plan at least a couple of days if you really want to explore all that is offered - highly recommended.