Melt 2 tablespoons butter in a 10-inch, straight-sided skillet over medium heat. Add garlic and next 3 ingredients; sauté 15 minutes or until vegetables are tender and onion is lightly browned. Add wine; bring to a boil over high heat. Carefully place salmon into skillet. Cover, reduce heat to medium-low, and poach 5 minutes or until salmon flakes with a fork.
Transfer salmon to serving plate; cover with foil. Increase heat to high. Bring mixture to a boil; cook, uncovered, 10 minutes. Pour mixture through a wire-mesh strainer, and discard vegetables. Bring wine broth to a boil; cook over high heat 3 minutes or until reduced to 1/2 cup. Remove from heat, and whisk in sugar, salt, pepper, and remaining butter. Serve sauce over salmon.