WASHINGTON — President Trump has spent the past week praising his new trade agreement with Canada and Mexico as a win for farmers, saying the pact will send cash pouring into the United States and enrich America’s agriculture and industrial workers.

“The farmers are so thrilled with the U.S.M.C.A.,” Mr. Trump said on Tuesday, referring to the new United States Mexico Canada Agreement. “We just opened up Mexico and Canada and it’s great for our farmers,” he said ahead of a campaign rally in Council Bluffs, Iowa.

But many are not ready to cheer.

American businesses still face a cloud of trade uncertainty as Mr. Trump seeks to replace the North American Free Trade Agreement, Nafta, with the new deal. The biggest concern: lingering tariffs on foreign steel and aluminum.

The metal tariffs, combined with retaliatory taxes that foreign governments have placed on American products, are undercutting the concessions that Mr. Trump won in the deal. While the new trade pact gives American farmers greater access to Canada’s dairy market and requires that a higher percentage of a car be produced in the United States, business and trade groups are raising questions about whether the agreement will actually deliver the economic boost the president promises.