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.