Steve,
My preference is D below, but usually, for me, it's not quite that "cut & dried", as the grain usually is something other then perfect edge or face grain. (I've never heard the term "leaf grain" before.)
Also, while the bend is more in one direction, in reality, it is bent in both directions, ie, vertically and horizontally to follow the shear.
I've sometimes had as much trouble getting the horizontal curve to match as the verticle curve.
I like to bend my rails over a form rather then the canoe, in part, because then I can better control the bend in both directions. (Plus I can continue to work on the canoe as the rails are setting.)
Dan