sample.php

<?php
// Trying to create a function to use wp_remote_post() instead of cURL. 
// Based off this example, http://developers.hubspot.com/docs/methods/forms/submit_form
public function send_hubspot_data( $first_name, $last_name, $email ) {
        $hubspotutk = $_COOKIE['hubspotutk']; // grab the cookie from the visitors browser.
        $ipaddress = $_SERVER['REMOTE_ADDR']; // IP address.
        $hs_context = array(
                'hutk'      => $hubspotutk,
                'ipAddress' => $ipaddress,
                'pageUrl'   => $_SERVER['request_uri'],
                'pageName'  => 'Checkout'
            );

        $hs_context_json = json_encode( $hs_context );

        // Populate variables with values from the form.
        $str_post = "firstname=" . urlencode( $first_name )
                . "&lastname=" . urlencode( $last_name )
                . "&email=" . urlencode( $email )
                . "&hs_context=" . urlencode( $hs_context_json );

        $portal_id = get_option( 'aj_hubspot_hub_id' );

        $form_guid = get_option( 'aj_hubspot_form_guid' );

        $post_url = 'https://forms.hubspot.com/uploads/form/v2/' . $portal_id . '/' . $form_guid . '';


        $response = wp_remote_post( $url, array(
            'method' => 'POST',
            'timeout' => 1000,
            'redirection' => 100,
            'httpversion' => '1.0',
            'blocking' => true,
            'headers' => 'Content-Type: application/x-www-form-urlencoded',
            'body' => $str_post,
            'cookies' => array()
            )
        );

    }

Exactly what I was looking for. Thanks for sharing!!