Never been to Jiangmen ~ Foshan is adjacent to Jiangmen! It should be about the same!
I am in Foshan ~ Sometimes I use Cantonese! Sometimes in Mandarin!
There are many positions that need Cantonese! I advise you to learn!
People in the service industry generally speak Cantonese! Some may not be needed!
If you were a producer, you wouldn't restrict the language!