Does the UK pension received in Canada have Canadian tax deducted already? or will I have to file a UK pension as income when filing the yearly tax return and paying tax on it?

HRMC are not tax collectors for the CRA

https://www.lethbridgeaccountant.ca/CRA.php

Your UK pension will be paid without tax being deducted by HMRC if the UK knows you have moved to Canada, because there is a Tax Treaty in place to prevent you being taxed twice, so it will be taxable in Canada and you need to declare it when you file your taxes.

These are the details. If it is like the UK, you don't declare to the tax authorities the amount that lands in your Canadian bank account but your UK entitlement amount converted into Candian dollars using the Bank of Canada exchange rate. Best to consult an accountant on this.

https://www.gov.uk/state-pension-if-you-retire-abroad

I declare the amount that lands in my Canadian bank account. If that's incorrect, and I've only this post to suggest that it might be, the difference between the amount declared and that suggested will be minimal. If there were to be an audit detailed enough to detect this misdeclaration, I'm sure I'd have bigger discrepancies to worry about.

It is not like the UK in that case. If a pension is paid out without tax deducted and deposited directly into a Canadian bank account on payment, the amount received is what is reported (line 11500 on a T1). If tax is deducted by a foreign government, the gross amount (before tax deduction) it is reported and a claim for foreign tax paid can be made on line 40500. CRA will determine if they will allow it.
If GBP is held for a better FX, the other consideration is any currency gain since the funds were received to when they are exchanged, which is unlikely to be a lot!
https://www.canada.ca/en/revenue-age...ax-credit.html

Hemlock, thanks for the clarification, this is useful information and makes life easier if you are in Canada. In the UK, to make matters worse, for reporting CPP/OAS, because the tax year ends are different, my CPP/OAS statement does not arrive until a month after my UK taxes have to be filed and I cannot access my Canada Service Account overseas. I would be interested to hear if anyone else is having this issue.