In Banana Fish, a number of Chinese American characters are introduced. The characters appear to come from a Cantonese-speaking background, based on what I have seen so far in vol. 4:
Golzine remarks that Lee is referred to as daai yan, which corresponds to the Cantonese for 大人. (The Mandarin pronunciation would be da ren.)
In the same section, Lee also tells Golzine that he provide the services of Yut Lung to him. This romanization clearly does not come from a Mandarin background, since Mandarin does not use non-nasal ending consonants (n and ng) outside of r. Yut Lung also corresponds to the Cantonese pronunciation of 月龍, which based on Golzine's remarks is the correct set of characters for the name.
Later on, we are introduced to characters with the names Yau-Si and Suk-Leui. Do we know the Chinese characters for these names and any others that may appear in the manga? I do not know enough Cantonese to be able to make meaningful guesses, particularly when Chinese names are rarely formed with coherent combinations of characters that make guessing easy. I tried the fan wiki, but there wasn't any information from a quick glance, and being only in the middle of vol. 4 currently, I didn't want to risk spoiling myself.