Good question; where are they?
Under the Canadian Charter of Rights and Freedoms, I have the right to be secure against unreasonable search or seizure, the right of liberty, and the right not to be arbitrarily detained.
In other words, I can't be stopped unless the Police / RCMP have a good reason for doing so, and they have to tell me what that reason is, immediately.
The problem with ID cards is that the Police find it both a lot easier to justify stopping you, and they have an immediate reason for detaining you for not having the ID in your possession. Doesn't matter that you left it in your other pants pocket, or you are wearing swimming trunks. Everyone on a nudist beach is now breaking the Law.
In short, ID cards are carte blanche for the Police to stop anyone they feel like stopping. Do the UK Police abuse Stop and Search rights? Ask a black guy.