If you are Canadian citizens travelling on regular passports no visa is required for visits up to 90 days. See Entry and exit requirements, https://travel.gc.ca/destinations/australia.
An ETA, (electronic travel authority) is required. An ETA is valid for 12 months permitting multiple visits of up to 3 months each. ETA are easily obtained using the official Australian government app. The government web page (https://immi.homeaffairs.gov.au/visas/getting-a-visa/visa-listing/electronic-travel-authority-601) suggests that most ETA are granted immediately.