ĉampano

The drink is named after a place and the place is named after a field. Champagne is Late Latin campania, open flat country, from campus. So a glass of ĉampano, a military kampanjo and a ĉampiono on a podium are all standing in the same Roman field, which is more than most etymologies give you.

Watch the capital letter, because Esperanto is strict here in a way English only half is. The region is Ĉampanjo and keeps its capital, because it is a name. The wine is ĉampano and loses it, because it is an ordinary noun and ordinary nouns are not names. English does the same trick with Burgundy the place and burgundy the colour, but inconsistently; Esperanto applies the rule every time. The rest of the capitalisation rules are set out in orthography and punctuation.

One note on quantity. Because it is a substance you measure rather than count, you will usually meet it after da: botelo da ĉampano, glaso da ĉampano. Botelo de ĉampano would be a bottle belonging to the champagne, which is not what anybody means.