I have the interesting experience of learning Wing Chun at Sifu Lo Man Kam's school in Taipei, where Sifu Lo (native Cantonese speaker) was always yelling the Cantonese terms at us non-locals, while the local students were usually using the Mandarin pronunciations of the same characters; and occasionally the the Taiwanese/Min-Nan (you can't really say Taiwanese = Fujianese, because Fujian has three major dialects) among themselves.
But the constant was definitely the characters. Though there are some characters that are commonly used in Cantonese that aren't used as commonly in Mandarin....
From a pronunciation POV, Cantonese and Taiwanese are much more "authentic" Sino languages-- compared to Mandarin, which has been influenced by the northern tribes. Supposedly if you read Tang poetry (from 1300 years ago), it's much more likely to rhyme in Cantonese and Taiwanese (and interestingly enough, Japanese "On" readings of the Kanji) than in Mandarin.
JK-
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