While applying for Study permit sometimes the visa gets a refusal for number of reasons. It normally happens when visa is applied without meeting all the requirements or when there is lack of proper presentation of the case.
Students from Visa –exempt countries normally require an Electronic Travel Authorisation (eTA) to visit Canada and can apply for study permit from inside Canada but the international Students from Non visa-exempt countries must prepared their application in proper way and must ensure that each and everything is taken care off before the application is send for visa. Visa officer looks not only for the strong academic record and the language proficiency but also for the finances available for their duration of stay and for the fee. Only those candidates who have presented their case well and have prepared a strong application with complete papers are issued Student Visa. Normally no interview is called and the assessment is based upon documents you have provide along with the application. So your application has to be perfect in all respects before you apply. Any misrepresentation can deny you a Student or Visitor Visa for ever. So be cautious before you apply.
There might be a screening or interview once you land in Canada. So you must be prepared well before you fly as any little variation in your credentials against what you actually say can put you in trouble. You need to make sure that everything is in order and you really understand what you have declared to the authorities while applying for Student Visa.
It will be very difficult to re-apply if the visa is once refused. As it remains it the records with the authorities so you need to make a strong case to defend your credentials and you might need some extra documents to support your case. It is highly recommended to put your case properly at the very first time so as to avoid such a hassle in future.