I used maple sap in place of water last year in a porter, and the flavor contribution was subtle, but this was a porter after all - easy to lose those subtle flavors. I did not add maple syrup to the secondary either. Aside from the roughly .07 gravity points added, there was maybe a faint woody flavor that was almost in the imagination more than on the tongue.
I would recommend an English style brown ale or a porter myself, because maple flavor would add complexity to these brews without clashing with the citrusy/flowery hops of American ales.