I have never paid extra for Elite Plus with Sunwing, but I did fly with them a few months ago and this is what happened....
My checked bag was fine. But my carry on was a bit heavy. The agent said "Put your makeup bag and toiletry bag in your purse! We don't count that in the weight..." So I did and I was ok. I'm glad I had room. She also said that they wouldn't be weighing any carry on luggage on the way home. (Not sure if that's standard or just at the airport we were flying out of.)
Anyway, once you find out the limits, know that they do abide by them.... but might be a bit flexible and give you some advice as they gave me.
For a charter airline, we were actually fairly impressed. It was a decent flight both ways. Far better than Air Transat.