Upvote:1
Firstly, if he got a stamp in his passport, that may be the easiest - have a look through his passport for entry stamps for August 2009, and that may give you the answer you're after.
Second option - try US Airways. With his full name, some other proof of ID, they may be able to locate the flight.
Thirdly - did he use a travel agency? They'll likely still have a record of the transaction.
Finally, if you contact Canadian Border Services they may have a way of identifying the date of travel, as there would be a record of him crossing their border.
Most of these will probably require some proof of ID, to be fair, but it should be possible to identify.