Today I went to vancouver consulate to apply for work visa, I got it. but I saw quite a few who applied for vistor visas got rejected. One thing they have in common is that they all spent very short time (less than 6 months)in Canada. Unfortunately I did not see any F1s. You are an F1 who is studying in the US which makes you a bit differnt from those vistors. My advice is : if you have financial sponsorship from your school such as scholorship/TA or RA with tuition waive, I don't think it problem, otherwise you will have to be very careful - since F1 does not allow immigration intent, you will be asked to show that you have strong ties (steady income, family members, business)to Canada, and I am afraid that you don't have much and you will probably be asked to go back to CHina for visa. Again, if you have scholorship, go ahead. Wish you good luck