I’ve been learning from the De Cymraeg course and there’s a similar construct I’ve encountered there that is something along the lines of , “Dyna oedd y lleiaf allai i wneud…”.
Yes, medru yn y gogledd, gallu yn y de. However as people move home because of work or whatever you’ll hear both everywhere. There are quite a lot of people who have moved from N Wales now living and working in and around Cardiff. Best to learn north and south variations if possible, there are lots of them. Some S & N examples which can be heard often:
Dere, Tyrd, (come, S & N).
Cer, Dos, (go, S & N).
(Personal forms).