Actually my 2-yr-old girl also have the same problem as yours, but we still insist to speak Cantonese to her at home. Even for my older son who prefers to speak English, I told him that he can only speak Cantonese to her as she won't understand if he yelled at her in English!
When she's almost 2, she started to like watching TV (she likes Barney and LeapFrog video). At the beginning, she preferred to watch the Barney video in Cantonese that my family bought from HK. Recently I realized that she likes to watch more cantoons in English, and she picks up some simple phrazes and can sing more and more English kids songs. I'm surprised that she can even say the phonic sounds of all the alphabets as she picked it up from the video.
I do understand your worry! When my older son started preschool at 2 when he didn't know any English, I picked a preschool where one of the teachers was orignially from HK in one of their 2-yr-old classes so she could speak Cantonese to each other. Maybe becoz of that, at the beginning my son always preferred talking to that HK teacher. Once she was in a break and not in the classroom, he felt a little insecured. But later on, he was ok with other teachers.