I know this will probalby be a strange and somewhat complicated question.

I just booked a one way ticket using Aeroplan miles from YVR via YUL to ZRH for my son and I, flying end of September.
Usually when checking in it is often required to show a return ticket when checking in with a Canadian passport flying to Europe, however, I am not booking a return ticket yet to limit any risk of cancellations due to the current situation and we are actually not sure yet how long we might stay in Europe.

Both of us have a Canadian as well as EU passport but on my son's ticket it shows his full name (including middle name) which is only in the Canadian passport since that is the registered name on the Aeroplan account.
So, here is the question, my son will have to check in with his Canadian passport since his EU passport doesn't have the middle name. If we are asked for an onward ticket will it be enough for him to show the EU passport which doesn't require the onward ticket or will we run into a problem if we get a very eager check-in agent?

Worst case scenario I have to either book an onward ticket out of Switzerland, probably to Germany, which I hope fulfills the onward ticket requirement, or call Aeroplan and change his name on the ticket without the middle name.

I know this is quite strange but want to make sure there won't be any problems checking in.