First major difference is pronunciation between Cantonese and Mandarin
Cantonese has at least 6 tones (some said 9 tones) while Mandarin has only 4 simple tones plus a neutral tone, which does not exit in Cantonese

Here’s the tone comparison between Cantonese and Mandarin:
Cantonese:fu1夫 fu2虎 fu3富 fu4扶 fu5妇 fu6负幸福=happy/happiness
Note that Mandarin xing4fu幸福 is pronounced as hang6fuk1幸福 in Cantonese (click for details)
Mandarin: fu1夫 fu2福 fu3斧 fu4富/负 xing4fu

Mandarin (or putonghua) is the standard and official language in mainland China.