Hi!
You did not write much about yourself, so I am not sure that anybody will be able to answer your question. Anyway, according to the information from CIC and also from various immigration forums, usually the best chances have people who has: good travel history/stable financial status/good work/family ties in their home country/property and so on.
I think it s good that you are a student. It might be a strong reason to come back - to finish your study. But again, it depends on the whole situation.
Make sure that U prepared all the documents thoroughly and carefully. Add some proofs of your relationship with your sister and her family-that would be helpful. Make a good and clear cover letter where you explain everything about the purpose of the visit, your relationship with your sister, your current status in your country and why you will come back home. It s like, you know, try to put yourself on the place of officer and answer all questions he might come up with in your letter.
That will increase the chances. They DO give visas if the application is clear and if the applicant is not lying!
Good luck!
