Mike is correct forget
The system operates just as Mike has described, with the pneumatic ram physically operating the same layshaft as connected to the main canopy jettison handle. The ram also withdrew the sear from the canopy jettison gun firing pin, which fired and 'blew' off the canopy. The jettison gun was actually affixed to the canopy itself, and located in a cupped socket on the canopy rail of the airframe.
The pneumatic ram was indeed connected to the door system, but on the opening side of the system, at 1200psi. The closing system ran at a further reduced pressure of 400psi.
Hope this helps.
Flipflopman