Check engine light on, code reading large air leak

Check engine light is on and a friend of the family who is also a mechanic told me the code pulling up is for a large vacuum leak. So, he had me replace the evap canister. He cleared the code and a day later my check engine light came back on. He explained it could also be a bad gas cap not sealing good. Or also a vacuum line but he said it would have to be 1 of those 3 things. So, I replaced the gas cap. Not even a day later the check engine light came back on. I visually checked the vacuum hoses and can't see any leaks. What else could it be? The car listed above is the Classic model. Thanks so much.