There is a valve inside the vapor separator. It's probably rusted closed and isn't venting the tank. Take the separator off and soak it in EvapoRust. It will attack the rust but won't touch the surrounding metal. That should free up the internal valve.
Once you have it removed, block three of the four nipples with your fingures. Blow in and out on the vapor line nipple. You should be able to hear and feel the valve moving inside. If you can't, it's rusted solid.
As long as the vapor line wasn't plugged, removing the charcole canister shouldn't cause your problem. You'd just be venting fuel vapors into the atmosphere instead of storing them to burn later.