If I were repairing it, I would make a reinforcement plate from 1/8" plate about 1" larger all the way around and weld that to the deck, cut off the bottom of the bracket by 1/8" to account for the reinforcement plate thickness. Weld all of the pieces all the way around with one pass of 3/32" 7018. From the photo, it looks like the bracket has been flexing under stress a lot so it broke in the heat affected zone. The repad will spread the forces out a bit and help keep the flexing to a minimum.
NOTE: repads need not be any thicker than the base metal but 1/8" plate is likely about as thin as you would find and should work well.