Combine 1 cup strawberry halves, 1/3 cup sugar, orange juice, vanilla, and lemon juice in a bowl, and mash with a potato masher. Stir in 2 1/2 cups strawberry halves. Cover and chill.
Preheat oven to 425°.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, 3 tablespoons sugar, baking powder, baking soda, and salt in a bowl; cut in margarine with a pastry blender or 2 knives until mixture resembles coarse meal. Add buttermilk, stirring just until moist (dough will be sticky).
Turn dough out onto a lightly floured surface, and knead lightly 4 times with floured hands. Pat dough into a 6 x 4-inch rectangle. Cut dough into 6 squares. Place 1 inch apart on a baking sheet coated with cooking spray. Bake at 425° for 12 minutes. Cool on a wire rack.
Split shortcakes in half horizontally using a serrated knife; place each bottom half on a dessert plate. Spoon 1/4 cup strawberry mixture over each bottom half. Top with shortcake tops; spoon 1/4 cup strawberry mixture over each top. Top each serving with 1 tablespoon whipped topping; garnish with whole strawberries, if desired.