This post is probably too late for the original poster, but hopefully it will help others. My fiance's mom had a problem with her Evap canister, so I did a little checking online. This seems to be a common problem and the EPA actually filed a suit against Toyota. It only applies to 1996-1998 models. It extends the warranty on the evap emissions control system to 14 years 150,000 miles.
Unfortunatly my fiance's mom's car is a 1999, so it isn't covered by the extended warranty. Apparently Toyota made some change in 1999 that got around the EPA's requirements, but they didn't actually fix the faulty evap system.
So the evap systems on 1999-2003 Corollas still fail prematurely, but are not covered under the extended warranty. Cost my fiance's mom a small fortune to have it fixed.
Other 1996-1998 models including the 4-Runner, Rav-4, Camry, Avalon and a few Lexus models are also included in this extended warranty. You can go to this website for more details. When you call Toyota about this extended warranty, they will deny that it exists. You have to be very persistant and refer them to the website before they will acknowledge it. Good luck.
Toyota Motor Corporation OBD Settlement - Compliance and Enforcement - U.S. EPA