I learned acient Chinese at school and many of the sounds are origially cantonese and being adopted to putonghua sound.
But in the modern Chinese, the written form of Cantonese only uses in Hongkong, although cantonese is spoken in the province of Guangdong and Hongkong. Cantonese in the mainland has many types of accents. Most people in the Mainland would struggle to read and understand the complicated form of Charater use in Hongkong.
So like many suggested here, if you are not staying in Hongkong for long, there is not much a point for your child to learn it. But she probably would develop an ear for it from people around her and watching TV.
A lot of expats in Guangdong would learn Putonghua because knowing this would get them futhur than cantonese.
Anyway, my 12 month old is exposed to English, Putonghua, Cantonese, a local dialect and German.
English-- mother to son, mum with
Cantonese--helper to him, helper with mum
The local dialet--my parents and relatives to him
German--mu husband's parents and relatives to him
We are trying to limit to two at home:English and cantonese. ( I would prefer Putonhua to be the other. But my currunt helper speaks it poorly. ) We plan to send him to an English medium international school here. (choices are very limited in this city in the Mainland. But prices are similar to those in HongKong)
If I were you, I would also keep it to two. Italian and English. Then learn the third for fun.