In the 5 years that start counting from the day that is mentioned on your visa, you need to be at least 2 years in Canada.
So for exemple: if the day on your visa is August 1st, 2010, you need to prove that you have been at least 2 years in Canada before August 1st 2015.

But!!! You need to land for the first time in Canada within 6 months following the date on your visum (so in my exemple you need to land in Canada before March 1st 2011).