Marineland is the most popular amusement park in Niagara Falls, Ontario. It offer an interesting blend of rides and aquatic animals (dolphins, sea lions, beluga and killer whales) shows. In the park's centre there is also a castle-like fortification that encloses deers to visit. Other animals that can be seen at Marineland include bears and fishes.
On a small note, you can get to have a view of the nearby Niagara waterfalls from the top of the Sky Screamer tower ride.