I saw a group of English tourists in the Luzern station trying to get to grips with their surroundings. The guy who looked like the leader said 'Ooooh look, they have a Co-op thing over there' (Pointing at Coop obviously)
Speaking English, to me I would pronounce it typically as 'Koop' and 'Migro's' so that's what I do.
On a tour bus last year, though, the guy told me it was 'Cope' and 'Me-grow'
Anything goes here anyway
Call it what you like, I don't believe there is a right or wrong in such a multi-cultural place.