This is a good question.

The answer is, it depends what you are trying to do.

For example, if you (or your parent) is trying to register for a program or get an ID that requires proof of citizenship, then yes, you need a citizenship certificate.

However, otherwise you do not need to have a piece of identification on you that proves your citizenship. If somebody is telling you that you need to prove your Canadian citizenship even though you’re not trying to apply for anything, they are lying to you.

You need to apply for a new citizenship certificate. You can do so by submitting the appropriate IRCC application form (available from their website) plus the form informing them you lost your card.

You will need valid government photo IDs and citizenship photos.

Once you’ve done that you can get your SIN card replaced.

Well, normally you would need to replace to your citizenship card with a new citizenship certificate. You could apply for urgent processing by showing you need it to apply for your passport.

However, given the pandemic, you’ll have to wait. IRCC’s processing has slowed to a crawl. We’re not even sure if they’re processing paper applications right now.

Let’s answer your two questions:

1. You are not supposed to have both. Moreover, you presumably need to submit the card to get ther certificate (unless you have some other proof of citizenship you can submit…)
2. For the SIN application, you just need your citizenship card or certificate. You can learn more about SIN applications here.

You need to apply for your citizenship certificate first. In order to do that you’ll need your mother’s birth certificate and your birth certificate listing your mother’s name, plus a photo ID.

If you were born in Australia, you will need to use the citizenship card to apply for the new citizenship certificate and the passport. (Citizenship cards were retired in 2012.) If you have only the photocopy you may have to provide other evidence of citizenship, such as a Search of Citizenship Records.

If you were born in Canada you can use your birth certificate.

You do not need to do anything to keep Canadian citizenship.

If you want to prove your Canadian citizenship, you can apply for a Canadian citizenship certificate (to prove it within Canada) and a Canadian passport (to prove it outside of Canada). You will need the certificate to apply for the passport.

You need to apply for your citizenship certificate. You need your birth certificate. You can learn more about applying for your first citizenship certificate here.

You need to apply for a replacement citizenship certificate but you need to make it clear that you are applying for it in order to apply for your passport. It could help to include information about passport requirements from your local Embassy/Consulate or a letter of explanation stating that you need to apply for a passport because you lost it.

So you can no longer get the old card; it was retired in 2012. You can amend the record and get a letter-sized citizenship certificate. In order to do so you will have to provide the legal name change and a photo ID in the new name.