Lol. If you are looking for little to no English, then GZ. But keep in mind that most people in China speaks Mandarin, and there are a lot of people in GZ that are from out of province. Chances are, you'll meet less Cantonese speakers than you would imagine. Lot of kids there don't speak legit Cantonese, school system forces them to learn Mandarin and parents are busy at work. Without a proper Cantonese education system, many of them are influenced by the Mandarin accent without self-aware. But in HK, unless you meet a foreigner, guarantee almost everyone you meet speaks Cantonese. Well yeah, then they have influences from English and Mandarin too. You'll hear the term "Lazy sound (懶音)" when you get there.

Oh, and then there's the different accents, different characters and different terms for "Cantonese" in Chinese. People call them different things over there: 粵語、廣東話、廣州話、白話、省話、廣府話.. and maybe there are others that I am unware of. 

:D

kc's ponts are totally valid. For China, the cities have a pretty high number of 'outsiders' (外地人), in the south mainly from Hunan and Sichuan. I haven't been to GZ for a while, but I remember that Cantonese is way more spoken there then in Shenzhen, were it seems 95% of people are 外地人. 

Once you leave the big cities then you usually meet more Cantonese speakers in China. Example, in Zhongshan the number of Canto speakers is much higher then in Shenzhen.

In Hong Kong the locals are not very used to speak cantonese to foreigners. But since you have been in HK already you probably know that, and know how to get around it. It should be noted too that many in HK do not speak English. 

2 minor points:

The Cost of living is MUCH higher in HK (even though CUHK is in the N.T.). You will spend a fortune on rent. China is way cheaper, the internet is terrible in China though (but then less distraction is good).

I would probably go to China and would do mainly self-study, making whatever I learn in school just 30% or so. And then travel around a bit in the vicinity (within the canto speaking areas). China has less distractions, making it easier to focus on your language goal. 

Hi Rob,  I agree that it is hard to engage hong kong people in Cantonese if you don't already speak the language . When I am shopping in the wet market and trying to practice my cantonese with Po Po , they often speak to me in Mandarin . Once I insisted in talking in Cantonese with a po po who sells flowers , she asked me in english : are you japanese ?   I guess  my cantonese is worse than their mandarin or english . :(

In my opinion, I think it's better to go to Hong Kong - as kc mentioned, the Cantonese is more "official" - when Guangzhou people speak Cantonese, there are definitely influences from Mandarin. That said, if you don't mind that, then Guangzhou can be a good place to stay as well. 

The reason I'm more inclined towards HK is because there are a lot of people who do speak English and are practically bilingual, so you can readily find a lot more people who can help you with English - Cantonese translation difficulties from an English vantage point.

In Guangzhou, however, you'll notice that the majority of the population does NOT speak English. You might have difficulty therefore interacting in your daily life practicing Cantonese, if you struggle with a certain expression, you'll find that perhaps if you phrase it in English, they won't understand you. 

If you're in HK, though, bear in mind that apartments are tiny, the food is quite expensive, and basically you'll need to budget at least HKD 10,000 or so per month, the majority of that going to rent and food. Depending on what other activities you're planning to do, you'll probably need more, so, hope that helps! 

Good luck with your Cantonese project, Rob ;)

Thanks Baggio. I think that too many people in Hong Kong speak English, and they will automatcally speak to me in English even though I try to engage them in Cantonese (they are being polite and I will follow suite - I am not assertive enough to try to continue in cantonese). I want to have no choice but to speak Cantonese, and I think my level is good enough now to immerse myself and leave English behind. Maybe we can chat sometime and you can assess my ability. Appreciate your feedback. All the best. Rob