| The Cantonese dialect is one of the major Mandarin dialects of China, it is spoken by a relatively large fraction of China's population. Cantonese itself has various regional dialects within the Guangdong province as well, although it is collectively known as Cantonese, many are quite different from each other. Most of these dialects have 9 tones, compared to Mandarin's 4. This makes Cantonese much more difficult to learn than Mandarin. Few foreigners use Cantonese as a "stepping point" into learning Chinese, most choose Mandarin because of both its relative simplicity and the use of pinyin. Once Mandarin is mastered, many Chinese dialects become easy to pick up.
Being raised in Hong Kong, I was taught the Southern Cantonese dialect, spoken in Hong Kong, Macau, and the lower parts of the Guangzhou delta such as Shenzhen and Dongguan. To non-native speakers there is no difference between the Guangzhou dialect and the Hong Kong dialect, but to natives there is a huge difference, the characters in the Hong Kong dialect being much more distinct and pronounced, the Guangzhou one a tad more sing-song.
As one proceeds North the dialects change rapidly, mingling with the next regional dialect, Fujianese / Taiwanese, a totally different language. I have no knowledge of this dialect, it might as well be Japanese to me. A significant local dialect is the Taishan dialect, used very often in America, because many of the original West Coast immigrants came from the Taishan area. Cantonese is possibly the most widely used Chinese dialect in America, as the Cantonese still dominate the Chinese immigrant community both numerically and politically. | 
