In a high kneel position the stroke is longer, the paddle is longer, and the
distance that the power traverls through the body to the boat is longer.
(usually seated, the hips or butt engage the canoe seat, and the drive is
transfered to the boat. This is fatiging at first. a sore back is common.
That said, the Olympic paddlers high kneel with a raised lower knee and are
quite fast.
A standard sitting position gives a quicker cadence as well as an easier
change of sides by occasionally changing sides- something not done as often
with high kneel.
Balance is different with each style. The sitting has a lower center of
gravity which usually equates with stability. However the higher center of
gravity of the high kneel actually slows the tipping and allows time for
another stroke. Visualize balancing an upturned broom in your hand, (high
c.g) and then an upturned spoon.(lower C.g.)..