The reason for the tariffs was to shut off steel imports of steel actually produced in China.
Mexico and Canada have obviously prevented the export of steel originally ladeled in China.
Wheat has been separated from China chaff
I believe that POTUS Trump lifted the steel and aluminum tariffs on Canada and Mexico because they have implemented controls to prevent China, or any other country, from dumping steel or aluminum in the U.S. through Canada or Mexico. If they are caught, the penalties would be severe.
I suspect the production costs of steel and aluminum in Mexico and Canada are aligned with production costs in the U.S.