Has anyone had any experience of a booking with one letter difference to the name of one of the passengers?

It's an extra "S" in the middle name of one of the passengers.

The complication arises from the fact it is an Air Canada flight booked through United.

United have said they cannot delete the one letter due to it causing a cancellation on Air Canada's side, but they have put a note on the reservation and this can be seen by airport staff and security and won't cause any issues.

Air Canada cannot delete the letter as booked through United, but then say that they cannot see any notes and that even with a note it can't be guaranteed we will be denied boarding.

Any experience of similar?

PS: I promise I did try and search for a name change thread first - thanks for merging.