Cantonese is spoken in Hong Kong, Macau, the Guangdong province of People’s Republic of China, as well as many overseas Chinese communities. Each of these regions has its own slangs and geo-specific terms. The translator of this edition is from Hong Kong; in general, the text can be understood by people from other Cantonese-speaking regions too.
Yes and no — it depends whether you are a politician or a linguist. Socio-politically, since Mandarin has been the official language of the People’s Republic of China since its establishment in 1949, regional languages are considered “dialects” by the government. Calling them distinct languages may be detrimental to the unity and solidarity of the state, which is worrying to those in power. However, from the linguistic point of view, Cantonese and Mandarin are mutually unintelligible, which means a Mandarin-speaking monolingual person, who has had zero exposure to the Cantonese language, will not be able to understand spoken Cantonese. The difference between Cantonese and Mandarin is comparable to that of Swedish and German, which are related but distinct languages. Even though Cantonese and Mandarin are both Sinitic languages that have the same ancestor, they have different sound systems, vocabulary and grammatical rules.
Cantonese is written in the form of Chinese characters, so Mandarin speakers can understand written words that are shared by both languages. However, some characters are unique to Cantonese, which means Mandarin speakers will not be able to understand them. Grammar also complicates the picture. When Cantonese speakers write, they can switch between Standard Chinese (e.g. for a newspaper article) and written Cantonese (e.g. for texting friends). This edition of The Little Prince is an example of the latter. Sentences are written in a way which reflects how Cantonese is spoken orally.