I will leave for Guangzhou next Monday.可不可以是 i want to leave to Guangzhou next Monday不行 leave for 是个固定用法那可以是i want to leave for Guangzhou next Monday可以，不过你这么说的话是中式英语。语法上没错。但是我的说法就表示 我想下周一离开去广州。不要看见“想”就用want