I have checked-in for 2 tickets on the same Air Canada flight.

My wife and I booked a personal trip YYZ-LHR in 2012 when a client meeting in Europe came up at the same time. I changed the return portion of the business trip to meet up with my wife and return via London.

However not wanting to entrust my personal trip in the hands of a client that might cancel at the last minute I maintained the personal booking so had a seat booked in Y and J on the return flight.

At LHR I checked in for both seats and was given two boarding passes.