'Канапка'! Не 'бутерброд'! :P 'Buterbrod' sounds like 'something disgusting'!!
Бутерброд is used throughout Ukraine, while канапка is a Western Ukranian word (although it is seems to become more and more popular in other regions too).
Both words are loanwords: бутерброд is loaned from German Butterbrot, and канапка is loaned from French canapé.