Why learn Cantonese when Putonghua is used all over China?
If you have a family connection for learning Cantonese then, by all means, learn Cantonese. But I would not hire a tutor and spend money to learn Cantonese, especially if it is for a nine-year old.
The China of 2023 is not the China of 1949 when Chinese were divided by geographical regions, and many still spoke dialects but not Putonghua. In the China of 2023, anyone who has a basic education speaks Putonghua.
The China your child will grow up and deal with will all speak Putonghua.