You can't come back legally with I-94 if visa is pending

If you go to Canada for the visa, your I-94 will be taken away from you. Therefore, you can't come back with I-94 while your application is pending. However, I heard one student came back without I-94, hiding in a car with other friends. But it is so risky that I would never recommend to any one. If you get caught, you are breaking the law.
Think carefully before you go to Canada. You might want to go to Mexico instead. Mostly you can come back to US if your visa was checked in Mexico. My student visa was checked 3 years ago in Mexico and I got back the same day. But I never picked up my visa as I don't want to go to Mexico agian for visa, not in this life.