Sounds to me like Sunwing mostly does charters anyway, rather like Swift. Maybe they have some kind of agreement with Swift/Apple/Eastern, but even if they don't . . . wet leasing out an aircraft is kind of what charters do anyway. (Swift also does damp leases, apparently, where you can rent the plane and pilots but use your own aircrew. Wouldn't be surprised if Sunwing does the same. And if one tour operator comes up short an aircraft on account of a D check or something . . . just damp lease one from someone else. Probably a lot cheaper than having an extra aircraft in your own fleet, even if you do have to pay the other airline's crew.)
So WG is using this plane daily on multiple legs, WQ needs another plane to fill their routes and presto, they get a WG plane. What do they do just pick up the phone and call? "Sure we can send one right over!"
At a wild assed guess? Yeah, more or less. The boss makes the call. The paperwork gets sorted out later. That sort of thing seems pretty industry standard in high dollar industries for really rush jobs with really big clients that you know can pay the freight. Just a guess, but that's about how I'd picture it. I expect if you own an airline you know who you can call to get a plane fast. You probably have them on speed dial and go fishing with them every now and then.
They only have 9 planes, 2 MAX and 7 800s. Seems like removing 11% of your fleet would cause havoc of daily operations for WG ops.
All of this seems incredibly byzantine. Sunwing Travel Group, the parent company of Sunwing Airlines (and a passel of tour operators, travel agencies, and hotels) is itself apparently nearly half owned by TUI. And they have a boatload of other airlines and their planes. (And travel agenicies, hotels, cruise lines, and . . . eegads.) Unless the slightly more than half not owned by TUI is all owned by the Hunter family and their holdings the group may be a de-facto subsidiary of TUI to get around Canadian ownership laws. (That sort of thing used to be remarkably common in Texas and Mexico.) In any case, I doubt they'd really end up short of airframes in a pinch. At they very least they have some big friends that they can probably call for a lease on friendly terms.
What the heck? I didn't think they started until next month. I really need to go back and check schedules.