Mandarin is the standerded Chinese languge.As you know,China has lots of dialects,Cantonese is one of them.But Mandarin the dialect which carried out by the Chinese government to the whole country.Cantonese can be used in Guangdong and part of Guangxin province and Hongkong and some other places,Mandarin can be understanded by the people in the whole coutry. :P Hope it can help.

Chinese Mandarin(普通话) is the language which is uesd as a native language in China; but Cantonese(广东话，粤语)is a dialect which is used in Guangdong,Hong Kong mostly and others^^ I can't say Cantonese,I am sorry~~Holp it can help you,thank you^^