Exactly :) the french word is "canapé", which we still use in these both meanings, although the "диван" meaning is the most common one. Like, someone inviting you to sleep at her/his house would gently precise that you will sleep on the "canapé" if he/she does not have another bed. So, don't expect to find mayonnaise on it, and if you do, no, that is not normal.
To finish with this, the word "canapé" on its sandwich meaning, refers to a particular one, close to the "tartine" or "toast": usually a small piece of support (soft bread, feuillettee, cuncumber...) with something slightly expensive on it. I suppose it was popularized through the royal court (with all their taste for special dishes, and, overall, special words). Some recipes that you'll typically find on people magazines ^^ Here is a french canapé: http://www.pretarecevoir.com/boutique/712-1035-large/canapes-tout-saumon.jpg And here is normally a sandwich for a french: http://i0.wp.com/www.marketfood.ma/wp-content/uploads/2015/04/sandwich-jambon-dinde.png?fit=700%2C400