From http://book.cakephp.org/3.0/en/orm/saving-data.html#saving-belongstomany-associations

new_gist_file.php

<?php
class ExamplesUsersTable extends Table
{
    public function initialize(array $config)
    {
        parent::initialize($config);

        $this->table('examples_users');
        $this->displayField('id');
        $this->primaryKey('id');

        $this->addBehavior('Timestamp');

        $this->belongsTo('Examples', [
            'foreignKey' => 'example_id',
            'joinType' => 'INNER'
        ]);
        $this->belongsTo('Users', [
            'foreignKey' => 'user_id',
            'joinType' => 'INNER'
        ]);
    } 
########################
    class ExamplesTable extends Table
{
    public function initialize(array $config)
    {
        parent::initialize($config);

        $this->table('examples');
        $this->displayField('id');
        $this->primaryKey('id');

        $this->addBehavior('Timestamp');

        $this->belongsTo('Users', [
            'foreignKey' => 'user_id',
            'joinType' => 'INNER'
        ]);
        $this->belongsTo('Relations', [
            'foreignKey' => 'relation_id',
            'joinType' => 'INNER'
        ]);
        $this->belongsToMany('VoteUsers', // changed Users to VoteUsers because conflict belongsTo Users
            ['className' => 'Users',
            'foreignKey' => 'example_id',
            'targetForeignKey' => 'user_id',
            'joinTable' => 'examples_users'
        ]);
    }