A decision and delivery of a Canadian study permit can take anywhere from 2 weeks to 12 weeks, or even months.
You can check the current average processing times on Canada Immigration, Refugees and Citizenship Canada website http://www.cic.gc.ca/english/information/times/, but the actual situation still depends your medical reports delivery, and/or any needs to verify your medical/financial/other documents.
As such, remember to always give yourself adequate time to prepare for any unexpected delay by applying as soon as possible after getting your letter of admissions from your university. Do not book air tickets based on your (or CIC website's) estimated processing times.
Once your study permit application is successful, you can plan for an early arrival in Canada if the need arises.