Is Cantonese a better choice in studying classic of poetry (詩經)?
Cantonese might preserve more sound distinctions than Mandarin, but they're both derived (as are most, though not all, modern dialects) from Middle Chinese.

The current consensus, arrived at slowly over decades, appears to be that Old Chinese was toneless; this doesn't mean that predecessors of the entering "tone" didn't exist, but there were more endings than the -p, -t, -k that are currently retained by various dialects.  It had many more consonant distinctions, which over time were replaced by tone contour in Middle Chinese and all subsequent dialects (including the Min dialects, which are not derived directly from Middle Chinese).

It is certainly the case that if you read 詩經 in Mandarin, you will lose many of the rhymes and other phonetic consonances.  Probably, if you read it in Cantonese, you will lose fewer, though not all.  But in neither case will you hear it the way it was originally pronounced.  None of Old Chinese is directly attested, not even in the fanqie way that Middle Chinese was, so we don't even know for sure what the phonetic realizations were (although we have a generally good idea of what the phonemic distinctions were).  But it almost surely had initial and final consonant clusters that no modern dialect retains.

Some good references in this area are Axel Schuessler's ABC Etymological Dictionary of Old Chinese, and William Baxter and Laurent Sagart's Old Chinese.  The latter even has a discussion of the effects of phonetic evolution on the pronunciation and rhymes of old poetry, and the authors are of course responsible for one of the prominent reconstructions of Old Chinese in recent memory.