TL;DR - possibly. Cantonese speakers have an advantage over Mandarin speakers in some areas, but it depends.
If you go through a general list of phonemes first, you see that Korean phonology is very different from both the phonologies of both Mandarin and Cantonese. But there are certain shared similarities in the phones which would give slight advantages to one vs the other:
- Korean 으 vs Mandarin i in zi, ci, si (Zhuyin: ㄭ) vs Cantonese Yale eu (as in 香). That's [ɯ] vs [ɨ] vs [œ]. I'd say Mandarin is closer here, but not really close enough to be useful for learners.
- Korean 어 vs Mandarin e (Zhuyin: ㄜ) vs Cantonese Yale o (as in 蔬). There's quite a bit of variation in how to analyse the Korean vowel, but that comes down to [ʌ ~ ɔ] vs [ɤ] vs [ɔ]. Cantonese is closer here.
- Standard Korean vowel length vs Cantonese vowel length. Mandarin does not have contrastive vowel length, but neither do most varieties of Korean anymore. Barely any advantage in Cantonese.
- Korean 외 vs Mandarin u(e)i (Zhuyin: ㄨㄟ) vs Cantonese Yale eui (as in 水). Again the Korean vowel has some variation, but [œ ~ u̯e] vs [wei̯] vs [ɵy̯] means that Mandarin has a slight advantage.
From a language learner's perspective, there is a contributing factor to "advantage" that can be as important - regular correspondences.
One of the most well-known similarities that Korean and Cantonese share with Middle Chinese but not with Mandarin is the range of 받침, or syllable-final consonants. However, one could easily point out that Korean ㄹ is similar to (Standard) Mandarin final -r, and that is missing from both Cantonese and Middle Chinese.
Rather, the advantage in the 받침 is the regular correspondences between Cantonese and Korean. This comes from the pattern of final consonants that both preserved from Middle Chinese, but that was lost in Mandarin (although there are clues, sometimes):
This correspondence only applies to 한자어 of course; Korean words ending with any other 받침 generally don't fall under the strict "classical" Chinese loanword form (although there may be other connections; e.g 붓 vs an earlier pronunciation of 筆 and 배추 vs post-classical early Mandarin 白菜).
Cantonese and Korean have both maintained the distinctions, albeit in different ways, and none has 100% of the Middle Chinese endings (compare 犯 in Cantonese faan6 vs Korean 범 with Middle Chinese (Pulleyblank) /buamX/, where Korean has preserved the ending better).
The fact that Cantonese has maintained these 받침 has also meant its speakers find 받침 in other contexts somewhat easier to learn than Mandarin-background speakers of Korean. This does contribute to an advantage in pronunciation that can be substantial.
Mandarin does preserve other features of Middle Chinese, for example the separation of retroflex vs alveolar consonants (翹舌音 vs 平舌音), and many of the rising diphthongs. But these are not as relevant to those who are learning modern Standard Korean.