Here are some more thoughts.
Free Trade currently exists between the US and Canada. A Canadian engineer is covered under NAFTA if he/she wants to go work in the US (and this is welcomed as there are shortages of engineers in the US). An American engineer is also covered under NAFTA if he/she wants to go work in Canada. The reality is, there is not a lot of cross border movement. People usually chose to work in an area they are familiar with. If you grew up in Houston, and went to school at Texas A&M, there is a good chance you will stay in Texas, and less of a chance you will go to Canada.
With regards to salaries dropping/rising. Well, this is a loaded question. If an engineer makes $4,0000 a year, we would say that this is a low salary. Would it still be low if say the annual household expenditure is $2,000 where this job happens to be? In that light, I guess not. You need to evaluate income and expenditure together, otherwise, you sort of miss the point. If I worked in LA, and lived in LA, I would probably ask (and hopefully get more in my salary), than if I worked and lived in Billings Montana.
With regards to living standards dropping/rising. Well, this is another loaded question. I don't know how I would answer that. There are several posts above that talk to this. My take is that Free Trade alone is not the deciding factor on living standards. The inner city slums in most major US, Canadian, English, French, German, Japanese, you get the idea, urban cities speak to the vast number of factors that affect living standards. I drove past the (I believe it was) Fireston estate about 5 years ago. All along the "notches" in the wall of the estate were "card board shanties". I guess that Free Trade doesn't really rank up there as to a cause for this discrepancy.
Is Free Trade good for America? For (put name of country here)? I guess it would depend on view point of the person answering. Just as after USC meets Texas to determine the number one team in the land, one side is going to be happier, one side is going to be less happier, and Penn State is going to be miserable because they weren't playing.
This last paragraph has a huge dose of tongue-in-cheek.