My in-laws are letting us use their Aeroplan miles our honeymoon but I'm not finding any decent flights when I try to book directly through the Aeroplan portal.

I'm wondering if it's possible to book a trip through, say, Lufthansa (their Star Alliance partner) and then upgrade to better seats at the airport with our in-laws' miles? The seats I'm looking at are upgradeable and we have access to their Aeroplan account, but not sure if Aeroplan actually lets do you do that.

Do we have any other options for an upgrade here? I tried searching on the aeroplan website but all I'm finding is the info for eUpgrades, which isn't an option.

Thanks in advance!