Are *A upgrade awards on AC (say, using SQ) available on all Y or B tickets (so long as any J seat is available) or is there a limited inventory (i.e. needs to be a mileage seat available or other bucket)? And does it automatically go from Y/B to J or is premium economy part of the equation? And is there a difference between using UA/SQ etc versus Aeroplan miles?
Trying to use SQ for YYZ-TLV which is notoriously stingy on award J seats (I believe max 1 per flight) and wondering if upgrade will work to go from Y/B to J. Thanks.