Thank you again everyone for all of the informative feedback. We're like jimmyvh in that we would be cruising outside of the summer rush. Being from Canada our summers from about June to September are usually very hot so there is no reason to escape.
Our most likely time to be looking at Caribbean cruises is mid January through March to break up our snowy Canadian winters. That's with the caveat that we'd avoid school March breaks, University spring breaks and any other holidays (ie Easter) when the ships would be more at capacity,