According to the World Factbook, the US has been Canada's top trading partner, having an import statistic of 73.7% and export 49.5% since 2011. It's likely that Canada exports so much to the US because it literally right on top of it; not to mention, the two countries share the same language (English) and have a similar political system, therefore they can easily commute with each other.
"During the first 5 months of 2010, Canadian export sales to the United States rose to US$113.8 billion." - Daniel Workman (Suite 101)
Top Imports
Small trucks
Medium size motor vehicle parts/automobile accessories
Aircraft and Spacecraft parts
Natural gas
In case you've noticed...
Canada and the US trade very similar goods, especially in capital goods, however, they continue a consistent pattern on trading with each other. The only thing that stands out from the US is the crude oil that they import from Canada, but other than that, it seems that they're just trading the same things; perhaps they specialize in certain parts due to the need for variety in consumer goods.
Top Exports
Crude Oil
Larger motor vehicle parts/industrial machinery
Natural gas (petroleum, potassium chloride)
Coniferous wood
Trading Agreements
North American Free Trade Agreement (NAFTA) - eliminates tariffs on Mexican imports and exports - rises living standards for Canada, the US, & Mexico
Canada-European Union - maintains good relations between Canada and Europe - boosts economic GDP - decreases unemployment
Economic Sanctions
Canada is not a target of any sanctions... they're too nice. However, as of July to December 2012, Syria has been receiving no assets from Canada due to "internal repression"- they had creating chemical and biological weapons with the goods that were exported to them.
"In response to the continued gravity of the situation in Syria, Canada imposed further sanctions against Syria under the Special Economic Measures Act. The measures further expand Canada’s targeted sanctions against the Syrian regime and those that provide it with support." - http://www.international.gc.ca/