To maintain your legal status in Canada, you need to ensure that the CIC receives your application before your status expires. For this you may consider using courier or online application.
A little bit good news is that, if your status expired during the suspension of postal services and the options above are not available for you, CIC will grant you an implied status for the length of time that postal services are suspended. In that case, you will be given a one-month grace period, commencing the date on which postal services resume, to submit an application to extend your status without having to restore your status.
So chances are, you may still have legal status in Canada. Temporary residents who need to renew or restore their status during this extraordinary period of time should talk to a counsel to discuss their options.