Chose a cage that is rectangular in shape. 24” wide or wider. Canaries need to be able to fly in order to maintain their health. Many references state 18” is wide enough, however, we have noticed that when we have our 36” breeding cages divided the 18” is not long enough to allow full flight. OK if it is only for a few weeks but not a lifetime. The adorable round “canary cages” are not appropriate for long term use for the same reason. You might have one on hand for “Photo Ops”, a hospital cage and a holding cage when the main cage is being cleaned. There are also transportation or show cages for that purpose.
Examples: Click on image for larger view.