Transport Canada commissioned studies before the provinces went ahead with the legislation. The studies conclude that the introduction of speed limiters set at 105 km/h increases safety in "uncongested region(s)." The maximum safety gains, though, were obtained when speed was set 15 km/h less -- at 90 km/h for uncongested volumes.
However, as the volume of traffic and percentage of trucks increased, the safety gains associated with limiters "become less pronounced."
More information can be found at:
http://www.tc.gc.ca/roadsafety/safev...iter/index.htm