You need an eTA if you’re a:

• Visa-exempt foreign national and you’re flying to or transiting through a Canadian airport
  • As a visa-exempt foreign national, you do not need an eTA (or a visitor visa) when arriving by car, bus, train or boat (including a cruise ship).
• Lawful permanent residents of the U.S. and you’re flying to or transiting through a Canadian airport
  • You must present a valid Green Card and the valid passport used to apply for your eTA at check-in.
  • you also do not need an eTA when arriving by car, bus, train, or boat, including a cruise ship.

You may be eligible to apply for an eTA (instead of a visitor visa) if you’re a:

• Citizen from UK and you’re traveling to Canada by air.
  • However, you still need visitor visa (not an eTA) when arriving by car, bus, train, or boat, including a cruise ship.

.Basic requirements to enter Canada

To visit Canada, you’ll need to meet some basic requirements, such as:

• have a valid travel document, such as a passport
• have a valid eTA or visitor visa
• be in good health
• have no criminal or immigration-related convictions
• convince a border services officer (BSO) that you have ties—such as a job, home, financial assets or family—that will take you back to your home country
• convince a BSO that you will leave Canada at the end of your visit

have enough money for your stay. (The amount of money you will need can vary. It depends on things such as how long you will stay, and whether you will stay in a hotel, or with friends or relatives.

Read more – https://www.visasrus.co.uk/canada-tourist-visa/