One of the most visited tourist attraction in Canada are the Niagara Falls. There are two (actually 3) waterfalls, the canadian Niagara Falls which are also called the Horseshoe Falls as well as the Niagara Falls on the american side which also include the Bridal Veil Falls.
Make sure to plan enough time when visiting the Niagara Falls, it can get very busy along the Falls as well as in the Town of Niagara, especially in summer.