Sounds like an interesting combo of chocolate and maple. And by interesting I mean, I'd love to try it because I'd never think to put those 2 together.
I am getting ready to do a choco-maple porter recipe that I found in the Brooklyn Homebrew recipe book. It also calls for maple syrup at the end of the boil... Let us know how it turns out!
That's the exact one that I made... I made a two gallon batch though. I will say this, I had to re-pitch the yeast because the first time it started from a slow fermentation to none at all. It's going good now. It was my fault though, I didn't cool the wort enough before pitching the first time or activate it either.
I made spent grain bread from the brew, turned out great i suggest you try it, here is the recipe.
Use brown sugar instead of white though.