Dave,
Our lakester has a canopy similar to yours. We have not had any canopy opening problems yet up to 250mph. We do not pressurize the cockpit directly. Instead we have a large NACA duct on the right side of the car which is plumbed to a Cup style blower and filter who's output is directly connected to the helmet. We did this to keep the old fat guys cool in the staging lanes not even considering the problems of blowing open the hatch with to much internal pressure.
POPS
575 A/GL