I can't help with the rails, but I'm building a Corsair and will have the canopy open when throttle is 25% or less AND the flaps are down. This is accomplished without requiring a channel just for the canopy. How can that be done you ask? Check out what Buz offers at Oregon Scale Aviation [link=http://oregonscaleaviation.com]Oregon Scale Aviation[/link]. The "Channel-3" product takes the input from up to 2 channels and activates a servo depending on the settings you program.

You can program it to open the canopy when throttle is less than 50% AND the flaps are 75% down or more, or when the gear are down and the flaps are 80% down, etc...

I have bought several of his products and highly recommend him.