This is a really interesting video by Professor Tang Keng Pan from the University of Macau. I had heard tidbits of this idea before, but he paints a clear picture of the connections between modern Cantonese and ancient Chinese— fascinating to know that ancient poetry (i.e. Li Bai, Du Fu) that is still treasured in modern Mandarin today, sounds even better when read in Cantonese.
The video is subtitled in Chinese and English. The University of Macao has a Facebook page with some other interesting clips as well.
Wordsummit 
It sounds intriguing and plausible.
Just as if one were to pick pronunciation of words from across the dialects of coastal China, it can be strung up to match Japanese prounciations in many words!
うそ❗️Is that really true? That sounds fascinating!
Well, for one thing the Cantonese way of saying “this one” (yi gor) is the same as the Koreans. Or how the numbers are pronounced mostly the same in Hokkien dialect and Japanese. So if you combine a little here and there you get quite some words that are pronounced the same! But this is to be expected since there has been many centuries of interaction of between people along the coasts and islands!