Answer:
manufacturers who export to Canada.
Step-by-step explanation:
From the question we are informed about an American firms claim that uses protectionism in Canada is on the rise as the Canadian government attempts to protect its infant industries. This protectionism will cause the greatest harm to manufacturers who export to Canada.
Protectionism can be regarded as economic policy that is used in restriction of imports from other countries using some methods and measures, these measures could be tariffs on imported goods as well as import quotas and some government regulations. This is usually create economic crises such as Great Depression.