Cantonese is a dialect spoken in Canton province, which Hong Kong is part of. So rural is not exactly the right way to put it.
If you think about it, there are more people outside of China speaking Cantonese than Mandarin. This is because most of the Chinese you meat outside of China did not come from mainland China. In fact, most of the Chinese you see are probably from Hong Kong.
Hong Kong being former colony of Britain did not have strict travel restrictions applied to those areas controlled by mainland China, and since it being a major trade route, many people were easily able to move to another location across the sea.
Most of the Chinese immigrants that worked for the western railroads in US are Cantonese people who settled in San Fransisco. And, because of this, most of the Chinese-Americans have their roots coming from Hong Kong, not from mainland China.
If you know Japanese by heart, Korean would be easier to learn, and vice versa. But Chinese is not going to be easy just because you are familiar with Chinese characters, especially if you are planning to learn Putonghua (or Mandarin as we called in our posts).
First of all, Putonghua uses simplified characters, which can totally mess up with your existing knowledge of Chinese characters. You basically have to relearn majority of characters (at least its not THAT hard if you are Chinese, but you are... not Chinese).
Grammatical difference between China vs Japanese + Korean are absolutely ginormous. So, if you are already having some difficulty with Japanese grammer, you are going to have double the trouble and possibly get things mixed up, which in turn hurts other foreign languages you already know.
But just because it won't be easier to learn, doesn't mean you shouldn't. Knowing Putonghua will allow you to have more business opportunities than knowing Japanese. Although, Japanese is essential if you want to consume content products produced in Japan without having to rely on other third party help (being able to directly consume content is marvelous), you are less likely to deal business with a Japanese person (or at least most, if not all, of those guys are educated enough to speak basic English), opposed to a Chinese person living in mainland China.