Soak cedar planks in water 30 minutes to 2 hours.
Meanwhile, pat fish dry with clean paper towels. Place, skin-side-down, on a large baking sheet; set aside.
In a small bowl, combine remaining ingredients; brush on salmon. Cover and marinate 30 minutes2 hours.
Prepare grill to medium-high heat. Remove planks from water. Place side-by-side on a hot grill. Allow planks to cook about 2-3 minutes. Remove salmon from marinade; discard marinade. Place salmon, skin-side-down, on planks. Reduce grill to medium-low and cover.
Grill salmon until it flakes easily with a fork (about 20-25 minutes). Have a spray bottle with water available to put out flare-ups on planks.