Yes, unanimous agreement is required once a country has applied, as part of the process of accepting the application.

However Article 49 of the European Union states: "Any European State which respects the values referred to in Article 2 and is committed to promoting them may apply to become a member of the Union".

So Middle Eastern and North African countries (and Canada) cannot apply in the first place.

I think Turkey is in the grey area that allows some wriggle room as it spans both Europe and Asia.