The phrase 順其自然 means trust nature to take its course in Cantonese, and every character makes sense except for 其. Can someone explain its meaning in the phrase? Thanks!
其 is referred to 'it' as in your translation. However, 自然 here does not necessarily mean the literal meaning 'nature'. Instead, it refers to the natural tendency of any subject you're talking about. If you see a child growing as he/she prefers to be rather than pushing him/her to be, 其is the child and 自然 means 'without intervention'. If you let something develop without attempting to change its route, 其 is that thing. In old Chinese, 其 as a personal pronoun is only one of its many senses.
What's more, it's a Chinese idiom, not just Cantonese.
As Stan's comment goes, 其 here simply means 'it' and refers to the subject of the sentence where the word 顺其自然 is used. E.g.
For that matter let's just leave it to chance.