For Cantonese people, which do you prefer as your second language?

Cantonese people live in the PRC, and the language preferred by the Central government is Mandarin (And it is the Language of the majority of the people - 850 million).

So, how does Mandarin compare to English as a second language?

Do Cantonese people prefer to learn Mandarin BEFORE English, as a second language?

Do more Cantonese people (Those living in PRC) speak English than Mandarin?

And yes I know Mandarin and Cantonese share the same character system, but I am asking about SPOKEN language

Thank you very much

Why is Mandarin considered such an important language?

I just don't understand why people regard Mandarin as such an important language. Sure, it's the most spoken language in the world, but outside of China, where else would you use it? If you got stuck anywhere in the world, chances are Mandarin won't help...