I would go for a little less than double. I put the recipe in Beersmith and came up with 6 lbs of Wheat. I thought 16 oz of Maple was excessive and would really detract from the beer making it VERY sweet, but that was my opinion without trying it.
The other malts could be doubled with no problem. It was slightly out of style guide in color, if that matters.
If you do use the syrup, I would go with 8-10 ounces by weight not volume. The hops should go to 1 ounce.
Again, this was using Beersmith with the American Wheat Beer Style -6D.