Probably not a good idea to try to use Canadian cash at any local Negril business. The business probably won't know the rate, or you could get a very poor exchange rate IF they are willing to do the exchange. Take your Canadian cash to a cambio and convert to Jamaican dollars; everything easy then.
Canadians should not convert CDN$ to US$ to take to Jamaica.(in my opinion). Why would anybody want to lose 2 to 3% on commission for that exchange? Changing CDN$ to J$ is easy at the cambios (and Banks).
And don't ever, ever change money on the street! (Jamaica 101)