Niagara Falls are on the Niagara River on the border of Canada (Ontario) and the USA (New York). More than 6 million cubic feet (168,000 m³) of water falls over the crest line every minute in high flow, and almost 4 million cubic feet (110,000 m³) on average. That is an absolutely stupendous amount of water!!
We went to the Horseshoe Falls viewpoint on the Canadian side first. There are really no words to convey how awesome Niagara Falls are, so let's get straight to the photos!
A panorama showing the view from the Canadian side...

Falls and spray...
The Maid of the Mist...
Water, water and more water...
Enjoying the Falls...
And just so you can feel like you're really there, I made a video compilation for you (click the "four arrows" button in the bottom right corner to view it full screen)...
Were you expecting the Falls to be so loud?! That much water makes a lot of noise!
For lunch, we met up with one of David's uni friends, Rupee, who lives in Buffalo, NY, but ducked across the border to meet us as there are more restaurants to choose from on the Canadian side.
When we left the Falls and drove up the hill into downtown Niagara Falls, ON, we were absolutely astounded by the tacky touristy-ness of it all. There was Madame Tussaud's, Ripley's Believe It Or Not, Hard Rock Cafe, haunted houses, theatres, museums, amusement rides, restaurants, hotels, casinos, etc etc etc, all lined up one after the other. It was like Dreamworld, the Las Vegas strip, and Times Square combined. Completely overwhelming after the natural beauty of the falls, yet just metres away!
Here we are enjoying lunch and great conversation at an Indian restaurant with Rupee and her gorgeous daughter, Nor...
Walking back to the cars...
Then, we crossed into the USA in convoy with Rupee (a surprisingly quick border crossing), stopped briefly at her husband's office in Buffalo so he could see David and Kela, and headed to the American side of the Falls (the park with green grass that you can see in the above photos and video).
Here are a few photos (the tall buildings across the river are near where we were for lunch)...

So, to answer the question of which side was better, Canadian or American... I think the front-on view of the Falls made the Canadian side incredible, but getting to stand really close to the edge of the Falls on the American side was amazing. So, go to both!
Here's a Niagara Falls fact for you: 15 people have intentionally gone over the Falls in or on a device (eg. a barrel), and not all have survived. The first person to do it, in 1901, was a schoolteacher... a female one... on her 63rd birthday!!! She survived but said:
"If it was with my dying breath, I would caution anyone against attempting the feat... I would sooner walk up to the mouth of a cannon, knowing it was going to blow me to pieces, than make another trip over the Fall."
After we left the Falls, we farewelled David and Kela at Buffalo Airport and then checked into our B&B in the pretty Elmwood Village area of Buffalo, NY.
The next day, Friday, our flight back to Seattle (via Chicago) left around 4:30pm, so until then we spent a relaxing day reading in a bookstore, driving around Buffalo admiring the city's beautiful old architecture, and finishing up our road trip snacks in a riverside park.
And that was our excellent 2-week road trip through east Canada! David and Kela, thanks for joining us - we loved travelling with you!
PS. More photos in our East Canada road trip Picasa album.