You can read the information from the QR code with any QR code reader. That's what the reader app does, and you can extract the data from the QR code. As the spec says, it is stored as a compact serialization JSON Web Signature, and the claims are also outlined in the spec. It will be signed by a key specific to the province, which will verify its validity. The data is in a standard format and should be able to be read with a little bit of programming, or possibly some sort of generic application which can read this data, although I don't know of any such generic application.
As to whether you can request that it be deleted, that is specific to your jurisdiction. In Canada, provinces are responsible for health care, so they may have the ability to preserve certain information for public health reasons, or not, which will depend on the laws in the province and nationally about how health data may be stored and maintained. You would need to inquire with the appropriate governmental body or an attorney to determine the laws governing that.
