>>I can't tell the difference between cantonese and mandarin orz.
You could, suprisingly easily, if you knew what to look for. Two easy ways to tell: there's no 'sh' sound in Cantonese, and barely any final consonants in Mandarin syllables: just -n or -ng, both of which sound more or less like nasalized final vowels in fast speech.
For more subtle differences that require some sophisticated eavesdropping and a good ear, Cantonese has more tones, syllable-initial ng, and a small majority of sentences end with the utterance 'ah,' which serves, among other things, to soften questions.
Oh, and completely subjectively, I find Cantonese sounds, well, a little less harsh than Mandarin. But you may disagree.