Canadian football vs North American football

Canadian football

noun
  • A game similar to American football played on a field of 110 yards long and 65 yards wide (with two 20 yard-long endzones) in which two teams of 12 players attempt to get an ovoid ball to the end of each other's territory. 

North American football

noun
  • Collectively, Canadian football and American football. 

How often have the words Canadian football and North American football occurred in a corpus of books? (source: Google Ngram Viewer )