Canada is around 3% of global market cap, and is heavily weighted in financials and energy. In addition, a significant portion of revenue produced in Canada is via US companies (i.e. Apple, Facebook, etc.).
Although the dividend yields may seem appealing, chasing yield is one of the biggest concerns in Canadian markets right now as investors who have shunned low-yielding bonds have bought up telecom and financial companies strictly for their yield.
The dividend tax credit could be changed at any time, especially worrisome considering Morneau is still in office (look what's happened to corporate taxes as an example).
Lastly, there are products which are great for non-registered accounts as they use total return swap strategies to effectively create only capital gains upon selling (which is a huge benefit for planning purposes) while providing exposure to non-Canadian markets.