Originally Posted by The Lev

Air Canada (like most airlines from North America flying to IST) has one flight per day to that city. For whatever reason they changed the departure time of the transatlantic flight to arrive earlier in the day, necessitating an earlier departure for you - but I'm assuming that your issue isn't so much having to leave earlier as arriving in Istanbul 5 hours before your Germany-based friend.

I agree with bawm that AC is being pretty reasonable about this: You can accept the new schedule or get a full refund and book on another carrier that better meets your needs.

In your situation, I'd look upon this as a blessing and take advantage of the earlier arrival to get a head start on visiting the sites, smells and sounds of a wonderful city and arrange to meet your friend at a hotel or other location rather than the airport. If you are connecting onwards, it still gives you a few hours to head in to the city. Enjoy the treat.

You could also call back and ask if they'd be willing to route you ORD-YYZ-Germany-IST. You might get lucky and end up on the same flight from Germany to IST as your friend. They are under no obligation to do this, but on days when AC doesn't fly to IST, they do offer that routing on their web site.