As a matter of policy we look at a number of comparators, including what other countries do, as well as the opportunities that Canadians have when they travel abroad. From our perspective, in terms of risk management—and I'm sure Bob would like to add to this as well—six months seems a reasonable amount of time to ensure that an individual is not planning to remain in Canada indefinitely and that the purpose of their visit is tied to a temporary stay.
We do have streams under permanent immigration for people to come for longer terms, including for work and for study. Essentially, this is a matter of policy, and we actually increased to six months from three months with the introduction of the Immigration and Refugee Protection Act in 2002.