Going from Tamil to Cantonese (粵語) has a composite linguistic distance of 91% (heuristic estimate). Below is the dimension-by-dimension breakdown.
Shared vocabulary, cognates, and loanwords.
Morphology, syntax, word order, cases.
Shared sounds and phoneme inventory.
Tamil → Chinese
Dravidian ↔ Sino-Tibetan
The 5 languages with the lowest linguistic distance from Tamil:
A quick 3-question check between Tamil and Cantonese. No signup.