Canary cages need to be large enough for your canary to fly around. Canaries are not climbers so it is important that they have room to fly. While canaries are a smaller breed you will still want to find a wider canary bird cage.
Ideally you want to pick a wider cage then a tall canary bird cage since canaries fly horizontally more than vertically. These little guys also like to hop from perch to perch so be sure and include perches in your canary flight cage.