They are the same. A walleye out of the southern USA is the same as a pickerel out of northern Canada.
In some parts of its range, the walleye is known as the walleyed pike, colored pike, yellow pike or pickerel (esp. in English-speaking Canada), although the fish is not related to other species of pikes which are members of the family Esocidae.
However the Wallye and Pickerel are distintly 2 different species.