From The Globe and Mail:

"Looking at the past 10 years, during which commodities prices were rising and Canada’s interest rate differential was mostly positive (i.e. Canadian interest rates were above those of the U.S.), the loonie has been trading almost exclusively above PPP levels. But now, these factors have changed, and are combining to bring the dollar back down toward or even below PPP levels within the next year or two. We have recently revised our December, 2014, target for the dollar to a range of 86 to 88 cents, just above the PPP level."

This makes a lot of sense, however, from a technical standpoint the CAD has fallen very far very fast which makes further downside much less likely over the near term:

CAD_Weekly_2.4.2014

The Canadian Dollar is extremely oversold on the daily/weekly timeframes which makes some consolidation between .89 and .93 likely over the near term. 

Related:

Low loonie, high energy prices boost Alberta’s bottom line

Plunging loonie hits consumer confidence