Last spring I was on an AC flight to the US. I forget the exact destination, but I think it was either RDU or CLT. In any case, I left my jacket on board, and since it was very warm where I was, I didn't realize what had happened until a couple of hours later.

I called the baggage desk and they connected me with somebody in lost and found. I was asked for the details such as flight seat number, description of the article etc. and by the time I returned to YYZ my jacket, and most importantly the little Pelican flashlight that I've had for years, was waiting for me. The outcome may have been different if I had lost a wallet full of cash, but personal items like a suit bag, won't have a huge amount of value so there is hope that your friend will recover his bag.

Good Luck

DF