I just checked the fine print at the Sunwing site. They only allow 5 kg for a carry on. If you go over that they will force you to check it at a rate of $10 per kg. All of it, not just the amount you are over. This is ridiculous as the lightest real carry-on bag that meets airline limits for size will weigh 3 kg empty. I have one that weighs 4.5 kg empty.
Sunwing is also the only carrier that does not cover your in and out airport tax in Dominican Republic. So, if you have a choice fly with anybody else. Transat, Nolitours, and I believe AC and Westjet do not have these ridiculous restrictions.