I agree. Just give it up. You'd be amazed at how well some Chinese people speak English.
LOL, I'm Chinese and I speak English.
Anyway, it's not worth the time you want to devote. Even after like 20 years, few English people can master Chinese well enough to sound Chinese (You know, those situations where others don't see your face, but they listen to your Chinese).
In addition, why learn Cantonese? IMHO, Cantonese is losing popularity. Almost every Chinese person understands Mandarin...but Cantonese....eh....uh....um....not that many people speak Cantonese.