Using the comments above, I've added the join to the Grid is pretty simple and straightforward way. To have the join, you cannot use Virtual type tables.

In your etc/di.xml add:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Framework\View\Element\UiComponent\DataProvider\CollectionFactory">
        <arguments>
            <argument name="collections" xsi:type="array">
                <item name="vendor_module_yourtablemodel_listing_data_source" xsi:type="string">Vendor\Module\Model\ResourceModel\YourTableModel\Grid\Collection</item>
            </argument>
        </arguments>
    </type>
</config>

Then, create the Collection, Vendor\Module\Model\ResourceModel\YourTableModel\Grid\Collection.php

and add the content below:

<?php

namespace Vendor\Module\Model\ResourceModel\YourTableModel\Grid;

use Magento\Framework\Data\Collection\Db\FetchStrategyInterface as FetchStrategy;
use Magento\Framework\Data\Collection\EntityFactoryInterface as EntityFactory;
use Magento\Framework\Event\ManagerInterface as EventManager;
use Magento\Framework\View\Element\UiComponent\DataProvider\SearchResult;
use Psr\Log\LoggerInterface as Logger;

class Collection extends SearchResult
{
    protected $_idFieldName = 'id';

    public function __construct(
        EntityFactory $entityFactory,
        Logger $logger,
        FetchStrategy $fetchStrategy,
        EventManager $eventManager,
        $mainTable = 'your_table',
        $resourceModel = 'Vendor\Module\Model\ResourceModel\YourTableModel',
        $identifierName = null,
        $connectionName = null
    ) {
        parent::__construct($entityFactory, $logger, $fetchStrategy, $eventManager, $mainTable, $resourceModel, $identifierName, $connectionName);
    }

    /**
     * @return Collection|void
     */
    protected function _initSelect()
    {
        parent::_initSelect();

        // Join the 2nd Table
        $this->getSelect()
            ->joinLeft(
                ['some_other_table_alias' => $this->getConnection()->getTableName('some_other_table')],
                'main_table.some_other_table_id = some_other_table_alias.id',
                ['some_other_table_column1', 'some_other_table_column2']
            );
    }
}

Flush the cache and it should work.

Using the comments above, I've added the join to the Grid in a pretty simple and straightforward way. To have the joined tables, you cannot use Virtual type tables. So, that's how you make it happens

In your etc/di.xml add:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Framework\View\Element\UiComponent\DataProvider\CollectionFactory">
        <arguments>
            <argument name="collections" xsi:type="array">
                <item name="vendor_module_yourtablemodel_listing_data_source" xsi:type="string">Vendor\Module\Model\ResourceModel\YourTableModel\Grid\Collection</item>
            </argument>
        </arguments>
    </type>
</config>

Then, create the Collection, Vendor\Module\Model\ResourceModel\YourTableModel\Grid\Collection.php

and add the content below:

<?php

namespace Vendor\Module\Model\ResourceModel\YourTableModel\Grid;

use Magento\Framework\Data\Collection\Db\FetchStrategyInterface as FetchStrategy;
use Magento\Framework\Data\Collection\EntityFactoryInterface as EntityFactory;
use Magento\Framework\Event\ManagerInterface as EventManager;
use Magento\Framework\View\Element\UiComponent\DataProvider\SearchResult;
use Psr\Log\LoggerInterface as Logger;

class Collection extends SearchResult
{
    protected $_idFieldName = 'id';

    public function __construct(
        EntityFactory $entityFactory,
        Logger $logger,
        FetchStrategy $fetchStrategy,
        EventManager $eventManager,
        $mainTable = 'your_table',
        $resourceModel = 'Vendor\Module\Model\ResourceModel\YourTableModel',
        $identifierName = null,
        $connectionName = null
    ) {
        parent::__construct($entityFactory, $logger, $fetchStrategy, $eventManager, $mainTable, $resourceModel, $identifierName, $connectionName);
    }

    /**
     * @return Collection|void
     */
    protected function _initSelect()
    {
        parent::_initSelect();

        // Join the 2nd Table
        $this->getSelect()
            ->joinLeft(
                ['some_other_table_alias' => $this->getConnection()->getTableName('some_other_table')],
                'main_table.some_other_table_id = some_other_table_alias.id',
                ['some_other_table_column1', 'some_other_table_column2']
            );
    }
}

Flush the cache and it should work.