I have QB online. I have a .QBB file from client How do I bring data into QB Online with no copy of QB Desktop?

Try restoring the QBB file on a trial license

https://quickbooks.intuit.com/learn-support/en-ca/getting-started/download-a-trial-of-quickbooks-desktop/01/262015#M1577

Then you may migrate to QBO from there.

https://quickbooks.grsm.io/Canada

If your QBB version is too old, you need to call and ask Intuit Data Service to convert it and get a QBW file to open on 2020 version. Should you need to resolve it in due course, consider purchasing a 3rd party conversion service.

Hope it helps.