Yes. When the retailer requires country of origin labelling and demands only U.S. beef, it's discrimination against all Canadian beef products.
The economy is so entwined that live cattle are also imported and exported. Currently, the level of U.S. cattle imported for feeding in Canada is higher than the level of Canadian cattle exported to the U.S. for feeding.
As such, it's important that products not be discriminated against at the meat counter.