two more questions

1. If I do want to take advantage of this opportunity to get multiple (or 2) entries, is the US embassy/consulate the only place(s) I may go apply for the visa? Another way to ask the question is, is there any way I can apply for this visa before I enter Canada?

2. if I do not want the multiple entries, and if I plan to come back to the US using my old expired visa with a valid I-94, does this mean that I do not have to turn in my I-94 during my flight to Canada?