Hello, I'm Keith and happy to help you with your question.
I assume that you live in the UK for more than 183 days in each tax year. In that case any interest you receive on your Canadian savings account should be declared to HMRC on your annual self assessment tax return. However, under the Double Taxation Treaty between the UK and Canada any tax deducted by the Canadian authorities is allowed as a tax credit against UK Income Tax, the purpose of the Treaty being to ensure that the same income stream is not taxed in both jurisdictions.
I do hope I have set your mind at rest on this matter.