Written Cantonese input?
Correct me if I am wrong, but I believe all Cantonese characters (theoretically) have pinyin representations. Examples:


冇 (have not) / Yale: mou5 / Pinyin: mao3
佢哋 (they) / Yale: keui5 dei6 / Pinyin: qu2 di4
咗 (similar to 了) / Yale: jo2 / Pinyin: zuo3
嘢 (thing) / Yale: ye5 / Pinyin: ye3


But in my experience, using a Standard Chinese Pinyin IME to enter Cantonese characters is just not natural. Sometimes characters are missing. Some commonly used characters are way down the list.

One solution is to use a Cantonese IME like this one. There are even online tools to input Cantonese.