This is what I have done in the past for routing to make it simpler / more streamlined.
(as a side note i used lodash here so if you aren't you can use native functions to do basically the same thing. lodash just adds a bunch of nice features / functions that you dont need to go write yourself)
in my routes.jsx file you should create functions that convert any parameters into a url with a default path for this answer lets just make one for a profile route
export function pathToProfile(userName, params) {
  return path(Paths.PROFILE, _.assign({userName}, params));
}
the path() function is just a simple helper utility function for generating a path. 
path(url, params, urlMap) {
  if(!url) {
    console.error("URL is not defined for action: ", params);
  }
  if(!params)
    return url;
  params = _.merge({}, params);
  if(urlMap) {
    _.keys(urlMap).forEach((k) => {
      params[urlMap[k]] = params[k];
      delete params[k];
    });
  }
  if(url.indexOf(":") !== -1) {
    url.match(/:([0-9_a-z]+)/gi).forEach((match)=>{
      var key = match.replace(":", "");
      url = url.replace(match, params[key]);
      params = _.omit(params, key);
    });
  }
  if(_.keys(params).length > 0) {
    url = url + "?" + this.paramsToString(params);
  }
  return url;
}
now looking at the constants file
Paths {
  PROFILE: '/user/:username',
}
Finally usage. 
I wouldn't recommend broswerHistory.push() when you can have an onClick handler. Yes it works and will redirect, but is it the best thing to use? react-router also has a Link that should be used wherever possible. you get some nice additional features one for example would be an active route for whatever page you're on.
browserHistory.push() is a good way to handle redirecting when you do things like an auth login redirect or if you are responding to data from a request and conditionally taking them to a page. 
<Route path={Paths.PROFILE} component={Profile} />
<Link to={pathToProfile(this.props.user.username, {myParams: 'here'})></Link>
what that would be translated into if you wanted to see the url from that exact link it would be /user/someUsername?myParams=here