Now it's morning. You said 3 things. Canada. Basement. Winter coming.
Do you have a woodstove? Here's what I'm thinking...
Basement. Concrete stores moisture like crazy, and so does the soil around it. Even the best sealed basements are not impervious. Unless that beauty is stored in a humidity controlled case, even as an electric it'll pick up moisture in the summer.
Heat. If you have a woodstove, it strips moisture out of the air. That's why we all put a cast iron kettle on the top. If you don't, perhaps you have a dehumidfier built into your furnace. Many homes with basements do. Or HVAC/Heat Pump/AC. Humidity suckers...
This may all be review, and I don't mean to be repeticious or condescending. I have a woodstove in WA, and it's been toasty every evening since mid-october. My workhorses are a Taylor 810, and my Tiger-ized Strat. The 810 gets Dampits in the Winter & goes in that excellenct Taylor case. I did it out evey couple of weeks, and re-wet the dampit. The Strat does pretty well, but in this season it'll need a quarter-tone of tuning a day...and by February a truss-rod adjustment...which will then need to be readjusted when the temperature comes back up.
My point...Dry heat really makes wood move. Especially, if it has been allowed to take on as much moisture as it wants in the summer. Finish really doesn't seal it as you might think, especially if it's Nitro. That may have been a one-piece topcap, that's just separated a tiny bit as the guitar has dryed out. If the guitar is less than 5-10 years old, it may just do this because it remembers being a tree. All those laminations in a guitar of that caliber are beautiful, but they were likey bonded with water-based Tite-bond. De-watering (the displacement of water as the solvent) of the glue, can mean many subtle changes.
I guess what I'm saying is...you may have stored this perfectly every day...and this still could happen. I think Matt Moriarity builds custom humidy controlled cases. But that is only a preventative measure, and no guarantee.
Sorry for the ramble...again.
"Hi Ho...the Carrion Crow...FoldeRoldeRiddle"