If your cabinets and floors will be maple, then I think your counters will be lonely without another grey to play with, so I'd suggest a tone of grey for the upper walls. If your trim has to be white, then I'd take the white onto the lower wall as well, as personally I find that a thin chair rail in its' own color looks skimpy, and prefer to see it take a lower wall from baseboard to chair rail into the world of a wainscoting, even if only via paint. I'd choose a grey for your upper walls in the same hue value as your cabinets, perhaps Benjamin Moore's Storm.

I'd also go out of my way to accessorize to bring your warm and cool tones together. Silver toned hardware will bring a bit of grey glimmer to the cabinets. A maple toned cutting board on the counter will bounce a bit of warm wood there. Perhaps a cork memo board in a silver frame, Pottery Barn's reactive dinnerware, or this casual set -- http://www.target.com/p/avanti-black-16-pc-dinnerware-set/-/A-11267913#prodSlot=large_1_18 -- you get the idea.

And if you have the wall space for an art piece, that's the place to cement your color palate.

Pics for inspiration... Gray can work with what you have-choose a warm gray. Also add some interest and sparkle with a backsplash... Good Luck! [houzz=][houzz=][houzz=]