Generally you have 24 hours to return to the airport for domestic flights and 7 days for transborder and international flights to report unnoticed damage to baggage:

If your bag is damaged, please proceed to the Baggage Service Counter in order to notify Air Canada/Air Canada Jazz in person before leaving the airport. Minor damage not noticed at the airport may be considered for repair if you return to the airport to report it within 24 hours of receiving your bag, or within seven days for international or trans-border itineraries.

However, your friend may be out of luck since AC does not accept responsibility for damage to wheels:

Despite care in the handling of your baggage, we trust you will understand that we are not responsible for the following: nicks, scratches, missing pullstraps, zipper damage, scuff marks, damage to wheels, soiling, manufacturing defects, damage resulting from over-packing or spillage of packed items.

You can get more details here and here here.