Spa grounding

Hi I am installing a spa in my back yard and am told I need to run a 6
gauge 4 wire cable to it with a GFI in a sub panel to be put outside
no further than 3 meters.
Now my question: Is the bare copper wire in the 4 wire cable enough to
ground the system, or do I have to run a separate insulated ground
from my main panel to this sub panel?
I live in Ontario Canada for code purposes.
Thanks