Canary is a very strong character. However, she cannot be poisoned in this stage, so she cannot deal much damage at the end. You can use other poison units instead in this stage.
I don't use Canary except for raids, hard story quests, and video stages, so if there are other units you want, I think it's a good idea to save up. Canary itself is a very strong unit, so if you have the space, I think it's a good idea to take it.
