Final answer:
Canada's primary contribution to the Allied air effort in World War II was providing skilled pilots who were integral to the RAF's defensive success, especially during the Battle of Britain.
Step-by-step explanation:
In World War II, Canada played a pivotal role in the Allied air effort by providing skilled pilots. A testament to this is reflected by the RAF's success during the Battle of Britain, where experienced Canadian pilots, alongside other Commonwealth members, made significant contributions to the defensive operations.
Canada's contribution went beyond providing manpower; it was also involved in the British Commonwealth Air Training Plan, which generated a vast number of trained crew for the RAF and other Allied air forces.