Free trade between nations is always accompanied by a few problems. Theoretically free trad allows the trading partners to maximize what each nation does best. In Canada's case, for example, free trade with nations that produce tropical or subtropical crops makes good sense as Canada is at a distinct disadvantage when it comes to growing bananas. However, Canada leads the world in the efficiency of its grain farmers who could export their crops in return for warm weather crops.
The trade does not only have to be in the form of raw materials either. Nations that see themselves only as hewers of wood and drawers of water will find that they are trading cheap raw materials for expensive manufactured goods. In the long term this is a trading strategy that will ultimately backfire. Until the recent increase in oil prices Canada's most important exports were manufactured goods. Long term focusing on manufactured goods and technological innovations is a much better strategy than relying on the export of raw materials; especially as raw material exports tend to fluctuate with demand and tend to take care of themselves anyway.
Canada's greatest mistake in terms of trade has been the policy that has encouraged foreign multinationals to develop Canada's most important resources. This has led to a situation in which there are very few large Canadian companies engaged in extractive industries and has resulted in huge amounts of money being transferred out of the country in the form of profits to foreign shareholders.
It is interesting to note that in the free trade agreement negotiated with the Americans in the 1980s, the Americans were very careful to make sure that they had unimpeded access to Canada's raw materials. This has not worked out all that well so far as Canada is concerned, resulting in a level of foreign ownership that few other modern nations would tolerate.