You can override 

>Magento\Catalog\Model\ResourceModel\Product\Collection class and join your custom collection with using **_initSelect()** function


Example:

                protected function _initSelect()
    {
         $this->getSelect()->joinRight(
        ['secondTable' => $this->getTable('custom_table')],
        'secondTable.id = main_table.entity_id');
		return $this;
		}