The pronunciation/accent, and slang of people on the street are different, and HKers mix in a lot more English words and phrases when speaking. Since I'd only ever learned HK Cantonese up to that point, I remember thinking that the first person I met from Canton was speaking Cantonese as a second language. (Mainly because her accent was so different from what I was used to.) However, my HK friends assured me that she was speaking "real" Cantonese, and that we were speaking Hong Kong Cantonese. That said, I recently met some people from Canton/Guangzhou and the difference in accent was much less noticeable to me than ever before. So, I've either gotten used to the sound of "real" Cantonese, or the two dialects have grown closer together thanks to improved communication, the internet, movies, etc. (It's probably some combination of the two.)

almost the same . maybe HongKong's cantonese is more standard but we can understand each other . so there are less influence in the choice of learning materials in Guangdong or Hong Kong.

yes but very minor, more or less similar or even minor than the difference between British English and American English. TV dramas in HK are all in Cantonese. My friends/students from Mainland watch them to assist in learning the language too.

I am sure there are... However, I can tell you some of the differences between HK and South East Asia... HK SE Asia Canton 廣東 廣府 Clever 叻 pan lay (don't know the characters) from Malay rice noodles 河粉 粿條 (gwai tiu [first tone]) Hokkien/Teochew influenced.

Hi im from hk :)oh yes there is a difference!! Basically we can understand each other.but the slangs in the two places are very different. We have 潮語 in hk(which means trendy vocabs) which i think ppl from other parts of china cant understand because of cultural background