It isn't.. RUN from that dealership he is full of ****.
its a canister under the car right behind the axle, almost against the fuel tank, probably need a tool to unclip it, ($less than $10) and then swap them quickly to not spill too much gas. (do it over a catch pan).
should be able to be done in less than half an hour, no engine tear down, no code, etc.
pictures:
http://www.aveoforum.com/forum/f94/f...2010-lt-12732/