Boeing 737-800 (C-GTVG)

It looks like this plane being rented from TrvelService - as per logo on sharklets and the paint over front doors

That's correct. For the winter season in Canada (October to May), Sunwing rents planes from Europe, in this case, Travel Service. For identity, they try to minimize expense by painting as little as possible. Sunwing also rents from TUI.