My French hovers somewhere between rusty and average, but I would pronounce it something along the lines of see-air-kle (although the "air" should be more like a flat 'e', as in how children first pronounce individual letters i.e.: not 'ee')

Mind you, perhaps you shouldn't listen to me. Last time I asked for bubbly on-board I mispronounced "Taittenger" as tatt-eng-er (I now think it should be tait-onge-ay).

"The champagne, sir?" came after a pause and a momentary blank stare.