Want to go to SFO or LAX in July and return via Canada. Notice that although CW seats are available I can't buy PE seats and upgrade with Avios on the outbound. Is the Avios upgrade option limited to the same seats that are available with full Avios too? Or is it just because it's the holiday and the upgrade option is blocked then? Pity there isn't a multi-city option for booking Avios flights.