Correct pronunciation for 北, 白 in Cantonese?
北 is definitely bak1. 

白 is baak6. 

I believe this b/p issue is probably just a romanization problem. Remember 北京 was Peking in times past. 

Words that start with b are usually represented by letter [p] in IPA and that is how many romanizations started, from IPA.

The Meyer–Wempe Cantonese romanization system is one such pinyin that does write the IPA initial [p] as p and not b.