No, a Cloud CVR cannot be reactivated.
If you've canceled Cloud CVR, follow the process to subscribe to Cloud CVR as a new add-on. Previously recorded footage cannot be restored.
This also applies if you cancel your parent plan (Cam Plus, Cam Unlimited, or Cam Unlimited Pro). Cancelling your plan will automatically cancel Cloud CVR. You can subscribe to Cloud CVR again once you have an active parent plan.