React+Meteor or React+Express(koa, sails etc) is what I think the question should be. Meteor is both backend and frontend, in this case, uses React as its frontend library. Flux is an architecture pattern much like pub-sub that React uses to organise its components in a uni-directional flow.
Meteor also exposes its API to the frontend. You would most likely do the same with express and expose an interface(JSON data or something) for React to connect to the backend.
But since I haven't personally dealt with Meteor more than just a barebones hello world and save something to the database, can't say more than this.