Private service, not a Government of Canada website. You may apply directly at Canada.ca.
For citizens of countries that normally need an eTA for air travel, Canada says an eTA is generally not required when arriving by boat or cruise ship. A valid passport is still required and visa rules remain separate.
If you fly to Canada or transit through a Canadian airport, an eTA can be required for a passport that is eTA-eligible even though another part of the journey is by ship.
For travellers from countries that normally require an eTA for air travel, the Government of Canada says an eTA is generally not required when arriving by boat, including a cruise ship. A valid passport is still required, and visa-required travellers may need a visitor visa.
If your passport normally requires an eTA for air travel, flying to or transiting through a Canadian airport can require a valid eTA even when the main holiday is a cruise. Check the complete itinerary rather than the cruise segment alone.
The outbound flight itself does not create an eTA requirement for leaving Canada, but the way you entered Canada and any earlier Canadian air transit still matter. Check the current entry rule for your passport and full itinerary on Canada.ca.
The Government of Canada currently charges CAN$7 for an eTA application.