As a useful thing to have, I've made rough measurements of the cargo area of the CX9 for my own reference. I keep them on my phone, so I reference what the maximum dimensions are when thinking about putting large objects in the car.
These dimensions measure the smallest/narrowest passages of the cargo area. I do not have the width of the area behind the 3rd row with the pockets. These may not be exactly what you looking for in terms of dimensions, but hopefully give you a better idea of the biggest "box" you could fit in the areas.
Here is what I have:
3rd row up - WxDxH - 43in x 16in x 24in (width of trunk opening, not into the pockets. Depth is kinda measured to the mid point of the seat back, since the seat backs are slanted. Height is roughly to the top of the seat back)
3rd row down - WxDxH - 43in x 40in x 28in (Height is from the cargo floor to the lowest part of the ceiling at the trunk opening)
2nd row down - WxDxH - 43in x 77in x 28in
long pole - 10ft