Why is there a caribou on the Canadian quarter?

Answer 1

There has been an image of a caribou, representing the large caribou herds in Northern Canada, on the reverse side of most Canadian 25 cent coins struck since 1937. There have been many commemorative Canadian 25 cent coins issued for special occasions that have other images, such as the Olympic rings, replacing the caribou.
The caribou has been an important animal in Candian history, as a source of food and leather.

By analogy, think of the US nickel issued from 1913 to 1938 which featured the image of a plains buffalo on its reverse side.