Hi, these are actually two different languages,Cantonese has its own grammar,pronunciation which is completely different from mandarin. I am Cantonese, I teach both Cantonese and mandarin to foreigner. Most of my students who learn mandarin with me found that difficult to understand Cantonese. However if they can speak mandarin, it would help them to understand some words in Cantonese. But to foreigner learning Cantonese would be more difficult than learning mandarin due to the tone.

It has some difference between Mandarin and Cantonese(wording, pronunciation and grammar). I am a Native Mandarin speaker and I use 3 years to understand Cantonese.

No. I’m a native speaker in both Cantonese and Mandarin. These are actually two different languages, they have their own linguistic systems despite the same Chinese characters. Personally speaking, I think Cantonese is more difficult than Mandarin for people to learn, since it has 9 intonations while Mandarin only has 4.

Most of them don’t understand the others, although these two languages are considered to be a dialect of the Chinese language.

These 2 languages aren't mutually intelligible.