The UK has already departed the European Union, although there has been no change in terms of travel as yet whilst the transition period has been in place. On 1st January 2021 this changes, the transition will have ended and the UK will be a 'third country', without the travel privileges of a member state.
The Canary Islands are part of the EU and the Schengen Area, as a result of Spain's membership. Although the Canaries have different customs rules, they are part of the EU in the same way as Spain for everything else.
It's important to check the official guidance on gov.uk in case there are any practical steps you need to take yourself. However, I wanted to raise one little known fact that could catch some travellers out. It is possible that you could be unable to travel for having too much validity on your passport.
Passports issued by third countries are considered to have expired once they have been valid for 10 years. And, of course, after the Brexit transition period, you will need to have at least 6 months' validlity left on your passport.
But the problems could come from the fact that the United Kingdom formerly issued passports with credit from the previous passport, up to 9 months. This means that British passport holders could renew up to 9 months early and have those unspent months added to their new document. Having those months beyond 10 years was not a problem while the UK was an EU member state.
A passport issued on 30th June 2011 with the credited months could therefore have an expiry date of 30th March 2022. For travel to the EU this would be unacceptable on 1st January 2021.
The EU will consider that passport to be expiring on 30th June 2021. But you would need 6 months' validity to travel, so therefore with that document you would be unable to travel on 1st January 2021 despite actually having 15 months left to run.
Check your passport with your travel dates on the gov.uk passport checker.