The US$ is fundamentally a weak currency. America's Net International Investment Position (the difference between its Assets and Liabilities) is at a staggering $ 8.0 trillion, by far the biggest in the world. Every year this number grows by at least 5% or $US 400 billion. At a certain point foreign investors will get tired or worried about too much US$ exposure in their portfolios and will demand higher premiums (which will be a combination of lower US$, higher bonds yields and lower stock prices). Canada's Net International Investment Position, on the other hand, is about zero. The C$ is fundamentally a strong currency. 

Moreover, Canada's financial sector is in a phenomenal shape. Banks, pension funds, insurance firms and government debt are all very solid. Very few countries can say this.