You'll first need to determine your residency status to see if you need to report your UK income on your tax return. If you are still considered a "resident" of Canada then you are required to report your World Income when you complete your Canadian Tax Return.
This link to the CRA information will help you determine that status: https://www.canada.ca/en/revenue-agency/services/tax/international-non-residents/individuals-leaving-entering-canada-non-residents/leaving-canada-emigrants.html
If you are required to report this income, you should use the 2018 UK Average of 1.7299 to convert the amount to Canadian dollars.
The Bank of Canada also has a currency converter which you can find here: https://www.bankofcanada.ca/rates/exchange/currency-converter/