Also do not forget tat Canton was the main port of the Tang Empire. Roads there from Chang An should have been well developed. Anyway as i said b4. The tang and other Han chinese from the north went tonthe south n diplaced the natives there. Hence the Tang language was bought into the south. The Tang n other han chinese need not assimilate the native language. Tang language replaced the southern natives. Hence tat is y Tang Poems etc sound better in Cantonese is because it is the closes language to the Tang. Southern languages did not replace the Tang. Its the Tang language replacing the southern languages.
guangzhou (廣州) was established as a prefecture by the han dynasty. similar to chaozhou, it was already a commandery during the qin dynasty. the area was commonly called panyu (番禺). it was formerly part of the nanyue (南越) kingdom, which includes vietnam today. it is not wrong to suggest that cantonese is actually closer to the vietnam tongue, as cantonese is a sinicized version of the ancient viet language. no doubt, it was an important port during the t'ang dynasty as persian and babylonian ships docked there way before the arrival of the portuguese. the persians at one time established a little enclave there during the t'ang dynasty, and actually brought in persian women to start families.