Upvote:3
Let me try to break this down for each segment of your journey:
London -> Europe
No exit controls in London, but your exit is recorded. I would show the Pakistani passport, and when asked for a visa, show your Canadian passport at check-in or when asked.
Europe -> UK
You can enter on your Canadian passport without issue. I would also show my entry stamp on your Pakistani passport to the immigration officer, and your proof of departure (such as a boarding pass) and ask them if everything is okay with your record.
UK -> Canada
Use your Canadian passport only.