get_pages Drop down list for selection of a page

1. You already have <option value="">...</option> you just need some extra attrs for it
2. You need to load current value and if value equals $page->ID than add attr selected="selected"

Here’s how it could be done:

<select name="easyreg_redirect_page"> 
    <option selected="selected" disabled="disabled" value=""><?php echo esc_attr( __( 'Select page' ) ); ?></option> 
    <?php
        $selected_page = get_option( 'option_key' );
        $pages = get_pages(); 
        foreach ( $pages as $page ) {
            $option = '<option value="' . $page->ID . '" ';
            $option .= ( $page->ID == $selected_page ) ? 'selected="selected"' : '';
            $option .= '>';
            $option .= $page->post_title;
            $option .= '</option>';
            echo $option;
        }
    ?>
</select>

where’s option_key you should enter options key where your value can be found ( where it saves it )

also, you could use wordpress selected function to write selected="selected", then it would be like these:

$option = '<option value="' . $page-ID . '" ' . selected( $selected_page, $page->ID ) . '>';