Ken in cold Saskatoon is worried that adding insulation to his attic will cause problems. The key is to insure that he has good ventilation coming in through the soffits and going out higher up on the roof.
In this segment we showed how to go into the attic to see if daylight was visible around the edge of the roof. The photo shows a view from the attic down out the soffits, where someone has a flashlight shining back up. If not, you could try a smoke source (one layman possibility is a theatre smoke machine -- firemen often have them to demonstrate fire smoke survival) under the soffits and watch to see if the smoke gets easily into the attic. If those two "non-destructive" tests don't work, you will probably have to open up the soffits from the outside and work on removing obstructions to the ventilation.
Ventilation baffles should be installed before installing new insulation is assure that the new insulation does not create a new block to air flow.