You must get an Electronic Travel Authorisation (eTA) to enter or transit Canada by air, unless you're exempt. Read the list of exemptions on the ETA website. If you enter Canada by land or sea, you don't need an eTA.

As a British citizen traveling from the UK to Canada, you must have a valid British passport (regular citizen status) and a sanctioned Electronic Travel Authorization (eTA). The eTA is linked to your passport and is required for air travel; it usually costs $7 CAD and is valid for five years. If you are a dual Canadian-British citizen, you must travel on your Canadian passport to enter Canada by air. For 2026, be aware that you may also be asked for proof of a return or onward ticket and evidence of sufficient funds for your stay. While a visa isn't required for tourism stays up to six months, if you plan to work or study, you must secure the appropriate permits well in advance. Always ensure your passport is valid for the duration of your stay; while Canada doesn't strictly enforce a "6-month remaining" rule for entry, many airlines do, so having at least six months of validity is a recommended "best practice" for any international journey.