you will need to show them any and all proof that you are not going to stay in Canada after you will finish your studies. examples of proof are properties that you own in Iran, employment; these kinds of things may convince them that you will come back after school to your home country. if this doesn't work, try to go to Canada as a tourist and when you get there, try to change your visa status by applying to one of the schools in Canada; by doing this, it may make it easier for you to get your student visa. but there's no guarantee. sorry i couldn't be more help.