The US can (and does) get by without French help these days. More recently, there'd be no France at all without US intervention in WW2.
Today, Canada would fall into an economic tailspin without its economic relationship with the US and would shortly become a geopolitical thrall to Russia or China (FAR worse geopolitical partners than the US!).
You are probably right, becauses we've become lazy over the past 40 years or so by focusing the majority of our trade on the US. I mean, it made sense. They were a massive market and a stones throw away. We had integrated transportation systems and a common language. But, the reality is that the US economy would also suffer without Canada's contributions. While we would likely suffer more, imagine we stopped shipping stuff to the US. Potash, energy, natural resources, aluminum. They would be pretty fucked. Not as much as us, but they would certainly feel the pain.
But, that being said, as we build trade relations with other countries or the EU, we can develop a more dynamic economy. Trade will never be zero with the US, but it will decrease.