I actually have a Maple Nut Brown on tap right now. It's quite good and very sessionable, but I would probably increase the amount of crystal if I did it again, to increase the sweetness a little bit. It's a little higher gravity than a proper "nut brown" at 1.055, but well within the standards of an "American Brown Ale" anyway.
What I made (adapted to 75% efficiency):
8 lb Maris Otter
9 oz Special Roast
8 oz Carastan
5 oz UK Chocolate Malt
4 oz Simpson's Extra Dark Crystal
2 cups Maple Syrup (grade B) at flame-out
1 cup Maple Syrup (grade B) to prime keg
.5 oz Mt. Hood (5.1% AA) FWH
1 oz Mt. Hood (5.1% AA) 90 min
WLP037 Yorkshire Squares Ale
OG 1.055, FG 1.010
Mash at 153 60 min
Fermented around 66F
You could just use another British yeast, since 037 is seasonal. Also, I would increase the amount of crystal by a half pound or so, maybe more. And maybe lighten up on the chocolate by an oz or so to lighten the color (I accidentally used an oz more than I wanted to). Still, this is a very good beer, that I have been preferring time and again to the other one I have on tap, an all-summit IPA that is also quite good (I'm very impressed with the depth of flavor I get from Summit hops).