GMC 2004 Canyon - Manual (Page 51)

The anchor points for the top strap on Crew Cab vehicles
are located on the back wall behind the rear seat. You must
pull the seatback forward to access the anchors.
Follow these steps to access the anchors and attach the
top strap to an anchor:
1. Release the rear seatback from its latches (B).
See Rear Seat Operation (Crew Cab) on page 1-9 or
Rear Seat Operation (Extended Cab) on page 1-10
for instructions.
2. Attach the top strap to the anchor (A).
3. Push rearward on the seatback until it locks into its
upright position.
Push and pull on the seatback to make sure it is
secured properly.
Crew Cab
1-45