Following Magento 2 guidelines, you should not use ObjectManager by yourself. Instead, you must use dependency injection. More info here
In your Block/Controller/Helper..., create a constructor and inject \Magento\Catalog\Model\Product\Attribute\Repository
class. For example :
/**
* @var \Magento\Catalog\Model\Product\Attribute\Repository $_productAttributeRepository
*/
protected $_productAttributeRepository;
/**
* @param \Magento\Catalog\Model\Product\Attribute\Repository $productAttributeRepository
*/
public function __construct(\Magento\Catalog\Model\Product\Attribute\Repository $productAttributeRepository)
{
$this->_productAttributeRepository = $productAttributeRepository;
}
Then, in your dedicated method, you want to call (PHPDoc added for clarity) :
/** @var \Magento\Eav\Api\Data\AttributeOptionInterface[] $manufacturerOptions */
$manufacturerOptions = $this->_productAttributeRepository->get('manufacturer')->getOptions();
You can now get options values and labels this way :
foreach ($manufacturerOptions as $manufacturerOption) {
$manufacturerOption->getValue(); // Value
$manufacturerOption->getLabel(); // Label
}