Based on the 7500 patents issued in 2008 up to the end of May, the following graph shows the prosecution time. Prosecution time is determined by calculating the time between the applicant requesting examination and issuance, measured in months (rounded up). The average prosecution time is 51.6 months.
Note that in Canada, examination has to be explicitly requested (with a fee) within 5 years of the filing date of the application. This means that ‘0’ in the chart is not necessarily the filing date of the application but is the time that the applicant requested examination. Also see my chart of prosecution time for patents by art class.