DR400 ditching
There is no way that I would jettison the canopy prior to coming to rest on the water, to do so is to remove the crews protection from a 30 KTS wall of water.
Knowing how the DR400 canopy jettison mechanism works I have no fear of it failing to work when required........... It is not like a PA28 door that can be jammed by airframe distortion if you fail to unlatch it before impact.