Third country visa in Canada when landing

I just got the Canadian green card and will land there in June and will be there for about 2 weeks to apply different . Now I am going to graduate school in US (2nd year). I came to US with a J1 visa, changed to H1 after 2 years and changed staus to F1 in 2004.

I have following questions.
1. If I don't apply new visa in Canada, can I come back with my I94 card? I am going to fly to Vancouver and then come back.
2. If I apply for the F1 visa in US consulate in Vancouver and get background check, I can still come back to wait or I have wait in Canada.
3. Will the visa office ask me to go back to beijing to apply for US visa?

Thanks in advance for all of the help.