You are being given a low exchange rate at HiLo if you use your cc. They convert your charges in J$ to C$. I could only give you US - J examples since I don't know what the Canadian - J exchange rate is. The rate they give you when converting $$$ is NOT in your favor, that's for sure. Unless Canadian banking fees are different, you're also being hit w/ a % fee for currency conversion regardless of the charge being in Canadian, US, or J$.
Mega Mart put through the charge in Jamaican dollars and my bank converted to CDN. The rate is very close to the rate I paid at the ATM & to buy the Jamaican dollars before I left. No extra charges, sure the conversion is buried in the rate, but that is also the case when I withdraw cash from the ATM. These are the rates I paid, not a big difference at the end of the day:
JA$ bought in Canada .011700
Scotia ATM wd in Negril .011002 & .011038
Visa charge (Mega Mart) .011037