Heavily grease a 12-inch round pizza pan and lower sides of a 46-ounce can. Place can, greased side down, in center of pizza pan. Set aside.
Combine sugar, syrup, and water in a small Dutch oven. Cook over medium heat, stirring constantly, until sugar dissolves. Cover and continue to cook over medium heat 2 to 3 minutes to wash down sugar crystals from sides of pan. Uncover; add peanuts. Continue to cook over medium heat, stirring constantly, until mixture reaches soft crack stage (275°).
Remove from heat, and stir in soda. Beat mixture constantly with a wooden spoon until golden in color. Quickly spread mixture on prepared pizza pan, and press to fit around can.
Cool slightly; carefully remove can from center. Allow peanut brittle to cool completely before removing from pan. Wrap in plastic wrap.