It is very common to write Cantonese songs in either Standard Written Chinese or Colloquial Cantonese. Both are sung in Cantonese pronunciations.
We only translate colloquial Cantonese dialogues in movies or TV. into Standard Written Chinese as subtitles, so the Mandarin speaking audience can understand the dialogues
We do not translate colloquial Cantonese lyrics into Mandarin, We just add a SWC lyrics beside the colloquial Cantonese one, or put SWC translation in brackets beside Cantonese terms that Mandarin speakers might not understand
Colloquial Cantonese: 邊有半斤八両咁理想?
SWC translation of Colloquial Cantonese: 那有半斤八両這麼理想?
Colloquial Cantonese with SWC translation in brackets: 邊有(那有)半斤八両咁(這麼)理想?
For Cantonese songs written in SWC lyrics, there's no need for translations
There are some Cantonese songs rewritten into Mandarin with completely different lyrics that's supposed to be sung in Mandarin. For example, 上海灘 has one original version that's in Cantonese and one Mandarin version that's sung in Mandarin