Using the option file you can send more configuration parameters to Saucelabs and Browserstack.

For example, if you are looking to run a test on a specific browser version ands timezone :

  1. Create a json  file with the following:
    {
            "screenResolution": "2560x1600" ,
            "timeZone": "New_York"
     }
  2. In the CLI, add  :  --sauce-options  "<aboveConfigFileName>.json"

SauceLabs

Add to your CLI:  --sauce-options  "config_saucelabs.json"

Example to the file:
All supported override parameters

{
    "version": 61,
    "seleniumVersion": "2.53.0",
    "screenResolution": "2560x1600",
    "timeZone": "New_York",
    "recordVideo": false,
    "videoUploadOnPass": false,
    "recordScreenshots": false,
    "recordLogs": true,
    "captureHtml": false,
    "priority": 0,
    "build": "build 4.5",
    "tags": [
        "tag1",
        "tag2",
        "tag3"
    ],
    "customData": {
        "release": "1.0",
        "commit": "0k392a9dkjr",
        "staging": true,
        "execution_number": 5,
        "server": "test.customer.com"
    },
    "maxDuration": 1800,
    "commandTimeout": 300,
    "idleTimeout": 90
}

Sauce lab options for params: https://wiki.saucelabs.com/display/DOCS/Test+Configuration+Options

Browserstack 

Add to your CLI:  --browserstack-options "config_browserstack.json"
All supported override parameters

{
    "project": "my project",
    "build": "build 4.5",
    "browserstack.debug": false,
    "browserstack.console": "info",
    "browserstack.networkLogs": true,
    "browserstack.video": false,
    "browserstack.timezone": "New_York",
    "browserstack.selenium_version": "3.5.2",
    "browser_version": 61,
    "resolution" : "2048x1536"
}

BrowserStack options for params:
https://www.browserstack.com/automate/capabilities

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