Does Stats Can have the percentage of overall Canadian sexual assaults that are reported to police from 1999 - 2009? For example, 36% of sexual assaults are reported to police, and 64% of them are not reported? I can only find stats on spousal sexual assaults in the GSS victimization surveys.
You will be able to get data on sexual assaults from the Uniform Crime Reporting Survey (UCR) -- in Summary Statistics on the Stats Can site, in CANSIM, and through the DLI. But those will not include non-reported data because how would you know what is not reported if it is not reported? I think your only approach could be to use surveys like the GSS that include variables on sexual assault and whether or not the crime was reported. For instance, the PUMF for GSS, Cycle 23 has the variable cir_d010 for "type of incident" (which includes "sexual assault") and another variable pfo_q100 for "Police find out about incident." There is also another variable pfo_q105 (How police learned about incident).
Furthermore, the following links may help you get an idea of how much is reported and what is not reported:
Violence Against Women: Statistical Trends http://www.statcan.gc.ca/daily-quotidien/061002/dq061002a-eng.htm
General Social Survey: Victimization
Measuring Violence Against Women: Statistical Trends 2006
Criminal victimization in Canada, 2009