I don't know if you have a purge valve of some sort or not on the sniper. The canister is very simple - the carburetor fuel bowl and the fuel tank were vented to it on the later cars. When the engine is running, you need a little air bleed sucking on it, and that's all you need. There was no control on it, no need for it. when you're driving, it sucks air through the carbon and eventually it dries out most of the gas that's stuck to the carbon. That's all it is.
If the sniper doesn't have some provision for "canister purge" specifically, then you could hook it to distributor vacuum advance and that work for the canister itself. That'll kill the advance signal, though, so don't do that if you are using a distributor with vacuum advance. If you don't have a good port for that, you could get some benefit by venting it inboard of the air filter. The air filter would have a little bit of pressure drop and that would make it pull a little bit.
I did some googling and I didn't find much. On the Dominator EFI, there was some discussion about creating a custom output, and using that output to turn on a solenoid valve in the purge line. If you can do that, you want to set it up so that it's only open above some non-idle RPM like maybe 1000 or 1500. That would then be able to run on manifold vacuum, which you hook as many things as you want to that.
