Depending on where you are flying from in Canada, Jamaica is getting to be on the outside edge of the fuel range of Westjet's aircraft. Therefore they have to be much fussier about the weight of cargo they are carrying. You might be able to make arrangements in advance with them to get the fee waived on the second piece of luggage, but if you have more than that to take, donation or not, they may not be able to accommodate you. Its a safety thing.