Canadians as a whole will always be better off if someone else wants to give us their stuff. Some small number of Canadians, it is true, may be hurt. The most we should ever consider doing when faced with other countries' suicidal approaches to their economies is to help those who were directly affected to move into more productive activities. In practice, this is a mistake too. Government is never capable of judging who is in need and how to help them.
Any attempt always turns into a form of welfare.
In truth, this is what protectionism is welfare for some special interest groups. Of course, it's not their entirely fault. They have been subjected to years of propaganda from teachers and the media. It takes a long time to drill the common sense out of a child. The proper Free Trade Agreement of the Americas is simple.