Spill lists 12 wineries in Oakville that confirm outdoor seating. Walk-ins are welcome at 1 of them, and 11 ask for a reservation. A typical tasting is $75.
Is outdoor seating at Oakville wineries first come, first served?
It depends on the winery. Many seat outdoors by reservation like any other tasting, and a few keep the patio for walk-ins. The winery's page says which, and weather can close a patio on the day.