給 will never be pronounced bei2. There can't be any confusion here. At least not in the minds of Cantonese speakers.
The reason you are confused is because you seem to assume that the only difference between Mandarin and Cantonese is a few odd sinograms here and there. There's more to it than this. These are two Chinese languages with differences that span grammar, vocabulary, and of course phonology. Why use 給, which is a "foreign", ie a non-Cantonese word, if you are writing in Cantonese, where you have 俾 and 畀?
Cantonese is often used, in a written form, by the government, public announcement and in advertising, at least in HK, when they want to make sure they reach the larger public. I see it every day in the streets, and in government buildings. It is also used online and in texting -- and there's also Cantonese poetry.