In Mandarin, when do you use 那麼 vs 這麼? In Cantonese, there isn't this issue since you just use 噉.
那麼/ 這麼 is the Mandarin counterpart of 噉 in Cantonese.
Example: 那麼辦好嗎? (is it okay to do it like that?) = 噉做好咩?
Example: 這麼辦好嗎? (is it okay to do it like this?) = 噉做好咩?
The difference between 那麼 and 這麼 is the proximity. We use '這' when the object is near you; and use '那' when the object is not near you.
'噉' in Cantonese doesn't make this distinction.
You can point at something right in front of you and say "噉?" which is from the point of your own perspective.
You can point at something in a distance and say "噉?" which is from the object's point of perspective.