There is no first-party solution for this yet, since React support came out in this release. Hopefully we can make it automatic in the near future. I think this is a key advantage of the Meteor model - since the parts of the stack are expecting to be used together, they can collaborate to achieve functionality like this isomorphic, re-hydrating, SSR.

There are already some community projects working on this functionality: https://atmospherejs.com/reactrouter/react-router-ssr