If you are applying via postal application, you do not need to send any originals at all..
You need to included documents that you submit via post as per the checklist (
https://www.blsindia-canada.com/toronto-jurisdiction/pdf/Checklist_Information_Booklet_for_OCI_2jun22NN.pdf ) and you have to self attest them.
The process begins by creating the application on the OCI website:
https://ociservices.gov.in/
In this you will provide the information mentioned in the sample application form:
https://www.blsindia-canada.com/toronto-jurisdiction/pdf/OCI-Sample-form-with-common-errors.pdf
Once you feed the required information you will have the upload your photo and signature on the OCI website.
Further on you have upload 3/4 different types of documents like Canadian Passport+Citizenship Certificate, Indian Passport+Surrender Certificate, Marriage Certificate, Employment Letter, Birth Certificate(only for minors) etc. (if you read through the checklist and sample forms you can figure the details) (these documents do not need to be self attested)
Once completed and submitted on the OCI, print the form along with the documents in the checklist, photograph (self attest the documents) and send the by Purolator