Most Cantonese speakers however, will have no problem reading written Mandarin because it's the standardized “written form of modern Chinese" taught in schools and most Cantonese songs nowadays are mainly written in Mandarin.

Pure Mandarin speakers with no knowledge of Cantonese will find it hard to read written colloquial Cantonese because of huge differences in vocabularies and grammar. It's akin to an English speaker with no knowledge in German reading written German. Occasionally you can guess the meaning of some similarly looking cognates (i.e. bier-beer, garten-garden, etc ) but comprehending the precise meaning of a sentence is often impossible.

Most Cantonese speakers however, will have no problem reading written Mandarin because it's the standardized “written form of modern Chinese" taught in schools and most Cantonese songs nowadays are mainly written in Mandarin.