open air cafe/alfresco dining are both outdoors but not necessarily on a sidewalk. go with sidewalk cafe, IMHO

http://www.merriam-webster.com/dictionary/plaza

Main Entry: pla·za
Pronunciation: \ˈpla-zə, ˈplд-\
Function: noun
Etymology: Spanish, from Latin platea broad street — more at place
Date: 1683
1 a : a public square in a city or town b : an open area usually located near urban buildings and often featuring walkways, trees and shrubs, places to sit, and sometimes shops
2 : a place on a thoroughfare (as a turnpike) at which all traffic must temporarily stop (as to pay tolls)
3 : an area adjacent to an expressway which has service facilities (as a restaurant, gas station, and restrooms)
4 : shopping center