Formal:
* 上洗手間 (seung sai tim gaan) - This is the most formal and polite way to say it. It literally means "go to the washroom".
* 上廁所 (seung ceh so) - This is slightly less formal than "上洗手間", but still polite. It means "go to the toilet".
Informal:
* 去廁所 (heui ceh so) - This is a more casual way to say it. It means "go to the toilet".
* 去洗手间 (heui sai sau gaan) - This is also a more casual way to say it, meaning "go to the washroom".
* 去方便 (heui foong bin) - This is a very informal way to say it, meaning "go to relieve oneself". It's often used between close friends or family members.
You can also use different verbs to express the purpose of going to the bathroom, such as:
* 上 (seung) - To go to, to get on
* 去 (heui) - To go
* 去 (heui) 小便 (siu bin) - To go pee
* 去 (heui) 大便 (dai bin) - To go poop
Tips for choosing the right phrase:
* Consider the situation and who you are talking to.
* If you are unsure, it is always best to use the most formal phrase.
Remember that Cantonese is a tonal language, and the pronunciation of each word is important. It's best to learn how to pronounce these phrases from a native speaker or a reliable resource.