French Bulldog (small dog) could have ridden in the cabin with his owner. Why was the in the cargo hold?
Probably just a little too big.
Maximum carrier size allowed
Height: 23 cm (9 in)
Width: 40 cm (15.5 in)
Length: 55 cm (21.5 in)
Maximum allowable weight 10 kg (22 lb)
Must be big enough to allow your pet to stand up, turn around and lie down safely and comfortably.
http://www.aircanada.com/en/travelinfo/airport/baggage/pets-in-cabin.html
Generally a French Bulldog is about 11 to 12 inches tall. Males weigh 20 to 28 pounds, females 16 to 24 pounds.
http://dogtime.com/dog-breeds/french-bulldog