Hi Simon the canister has this function:
stores crankcase fuel vapours when the car is switched off and then draws it back in again to be used in the combustion process
I think you will have to trace the pipes,the supply pipe runs from the tank to the fuel filter,and the return comes from the engine,the third pipe is a breather pipe which runs to the charcoal filter which I think is situated near the drivers side front wing.The pipes are under pressure,but once released there should not be so much petrol running. I personally wouldn't cap the breather but get a good second solenoid. Also if you have a corroded pipe, other owners have found using stainless steel central heating pipes is an adequate replacement. And the clips you should be able to buy from any motorfactors.
You might be able to get the parts from Audi as a set assembled and I believe they are a complete pain the rear end to fit as they go behind the steering rack.
I've also seen on the s2 forum that owners just remove the canister completely but how this would affect emissions I'm not sure.
S2 owners have also: Just plug the hose that enters the IM, so you don't get a boost/vacuum leak. Leave the N80 pluged in or you'll get a fault code.
Then go to the boot and you'll see where the pipe exits the tank breather to go to the front of the car, disconnect that and replace it with a hose that will be the new vent. I routed mine out the air vent in the boot, so the fumes exit behind the rear bumper.