A code P0442 is NOT necessarily an EVAP Canister fault. A code P0442 is a small EVAP SYSTEM leak, so you need to find the leak. On GM, I go to the canister purge valve and do a vacuum holding test first and foremost. I do Emissions work in Calif, so please don't assume that a code P0442 is a leaking Canister. Did a parts store tell you this?
here are some shops: