Moderator, Air Canada; FlyerTalk Evangelist
Join Date: Feb 2015
Location: YYC
Programs: AC SE MM, FB Plat, WS Plat, BA Silver, Marriott Plat, Hilton Gold, Accor Gold
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You may also want to consult the UAMP forum to see whether this might open up any other options for you, such as a change to a more direct routing on UA metal, or a different flight on that Wednesday.
Aeroplan has wide latitude to open up space on AC metal in cases like this; not sure what UA does for MP.