Cache is spotlighted in...A Geocaching Blog from Opencaching North America - 10 April 2013. The blog post actually details four ways to complete the requirements for this virtual in more detail than I initially did below, so you may wish to check it out.
I visited Niagara Falls during my stay in Western New York for GeoWoodstock IX, over the Canada Day / Independence Day weekend, 2011. My son and I took the Maid of the Mist ride to get a look of the falls, up close. I can't recommend it enough. If you ara at or near Niagara Fall, you need to experience the falls in this way.
Though the cache is listed as being in New York, you can complete this virtual cache, from either Ontario or New York, without the need for a passport. The Maid of the Mist is the only tour service that offers a view of the Falls from the water and operates between April and October, from both the US and Canadian shores. There is a fee to take the boat ride. Follow the previous link for current prices. The Maid of the Mist boats are are wheelchair and stroller accessiblee.
If you have another legal way to access the lower river, you are free to use it. I would not recommend taking a barrel over the falls, though.
LOGGING REQUIREMENTS: Simply take a photo of yourself and / or your GPS with the Niagara Falls in the background - from the water, below. Your photo does not need to be taken from the precise coords. Additionally, you may include either the American or Horseshoe Falls in your picture.