Due to the detrimental impacts of COVID-19 including its travel restrictions to the US-Canadian border, you cannot travel from inside Canada to apply at a port of entry.
As a result, visitors can extend their stay by applying for a visitor record to extend their stay. Workers and students have two options. If you are no longer studying or working, you can apply to change your status. If you want to continue working or studying you can apply for a work or study permit extension.