The M910 XTR levers were only available as a brake/shifter combo, and were only suitable for cantilever brakes.
V-brakes were introduced with the M950 groupset.
So cantis it is.
I used m900rapidfires witch 1st XT V-breakes
Works good, but You have to expect deep and soft breake (when You will use breakes hand will be closer to bar than witch cantis)