So if a BA 380 does a missed approach at YYZ, for example, they must divert to YVR?
There are a few suitable airports across the border that would be more practical than YVR
Because of taxi/gate/runway restrictions, A380 operators provide their crews with categories of airport to consider for diversion. Broadly:
a) Any time
b) Not ideal but you'll get off the runway and be able to park somewhere and takeoff again. Passenger handling might be very cumbersome.
c) Only if the proverbial excrement hits the fan, as you might not be able to get off the runway, park or takeoff again. But you'll land safely.
Medical facilities will also be categorised to help the diversion decision making process.