The last several years have seen a strong separation between Canadian equity returns and US equity returns, made even stronger by the Canadian dollar's outperformance as well. EWC is an iShares ETF that measures Canadian equities (in US dollars), and SPY is a good ETF to reflect US equities. The graph below shows the ratio between these two ETFs, highlighting the strong out-performance Canada has had for almost 13 years now.
The interesting question is, can a difference like this continue for long? The ratio has clearly had trouble going over 0.25 since mid-2008, and from the craze for commodities that has been behind this trend, I would be very worried about investing in Canada assuming this ratio can continue.
It's too bad this data isn't available for the seventies (the last big commodity surge). I suspect it would show a similar run-up followed by a drop to the 0.1 level that you see in the 90s. What and when will make it fall is impossible to predict, but some things that come to mind are a hiccup in China's debt-fueled growth, increasing interest rates causing construction slowdowns around the world, etc.