Squaremouth.com
is a website that offers travel insurance plans from many different companies and many different levels of insurance. You can compare coverage and costs over a wide spectrum of alternatives. That is where I buy our trip insurance every time. I have never needed it, but, as my Mother used to say (over and over), "You never know".
Also, if something should happen, you might have to pay for the medical expenses in Jamaica and then get reimbursed from the insurance. I'm thinking that might be how it is if US/Canadian insurance is not accepted. Bring credit cards with lots of limit and save your paper work.
Because, "you never know".