If we take Guangzhou to represent Cantonese and Meixian to represent Hakka we can get an idea.
Sentence intelligibility test
The standard for mutual intelligibility works like this:
If two languages are 80% intelligible (or more) with each other, then they are dialects of one language rather than two separate languages.
These two certainly don't meet the requirements.
It seems that Hakka speakers can understand more Cantonese than vice versa.
If you'd like to know more about the intelligibility tests you can check out this PDF here. Where section 3.1. Isolated-word-intelligibility test goes over table 2 and section 3.2. Sentence intelligibility test goes over table 3.