I would say not a Marans, but I don't have the cuckoo variety. I'm no expert but it looks nothing like my coppers (shape wise?) and the feathers don't look like they are the cuckoo pattern to me.
I'd say its a light Brahma, if those are the only 2 breeds it could be, and it looks like one to me that beak seems to support that...and its looking a little red but maybe its the light?