Hi Canadiangirl78,
Because I currently live with my husband in Toronto, Canada, I did the following:
1. I sent my application for permanent residence to the Mississauga office.
2. My husband applied to sponsor me at the Mississauga office as well. Which was approved.
3. My file was automatically sent to the Buffalo office. I guess this was because we live in Toronto. Buffalo happens to be the closest office outside of Toronto, Canada.
Good Luck