Monthly security updates will come from Google (for all models), and system updates will be managed by Verizon for Verizon models, and Google for unlocked models bought from Google Store.
Pixels bought at Best Buy are the Verizon models, so system updates for those, too, will be managed by Verizon. Combined with the news that Verizon models will have a locked bootloader and come with Verizon crapware, it's pretty clear that Americans among us should really, really opt to buy the Pixel outright from the Google Store. Yes, that means higher upfront costs, but you'll have lower monthly expenses, proper updates, and an unlocked bootloader.
Anybody with even an ounce of common sense should avoid Verizon Pixels like the plague.