With Bill C-22, the government would hold the copy. The lock you trust would no longer be a lock only you can open. It would be a lock the locksmith was ordered to duplicate.
I don't think this analogy sells just how bad this is. Building a backdoor means fundamentally weakening the encryption. Instead of having an extra key it's more like building a lock with a concealed button that lets you completely bypass it and open the door, and then just hoping nobody finds it besides the 'right' people (i.e cops and gov).