In both World War I and World War II, Canadian forces fought on the side of the Allied Powers. There was, however, a difference in Canada's status in those two wars.
In World War I, Canada was not a fully sovereign country. Instead, it was a dominion of Great Britain. As such, it was obliged to go to war when Great Britain declared war.
In 1931, Canada became a fully sovereign country. Because of this, Canada particiated in World War II of its own accord. Canada took its own vote in Parliament to declare war on Germany (and later on Italy and Japan).
So, Canada was on the same side in both wars, but it was only in WWII that Canada's own parliament voted to participate in the war.