Confusion on where to send outbound application.

[Cluostari]

I got a hold of the CIC earlier today to ask them what to put for requested processing office on one of the forms and they told me to put Buffalo(I'm American).  But my common law spouse told me that the forms she has to fill out tell her to send it to the Canadian visa office.  So who do we send everything to?  Mississauga?  Or Buffalo?

[Kaycee1]

It's a 2 part process. You send everything to Mississauga - they do the approval of your sponsor, to say that she is eligible to sponsor you. Then the Mississauga office will forward everything themselves to the appropriate Visa office - in your case Buffalo. There they do the 2nd stage of the process, approving you to be a permanent resident.

[Maid_Marian]

Yeah, it is confusing! Kaycee's completely right though: regardless of where you're being processed (I'm going through London), everything goes to Mississauga (CIC-M) first, where the sponsors are assessed before the whole package is sent on to whichever centre is yours.
Some people have a choice and this is where Question 6 on IMM 1344 (your partner's form 'Application to Sponsor and Undertaking') comes into play. For me, I've been living in Canada a year now, so could process through Canada, but we've chosen to go through my country of nationality (London) rather than my country of residence (Canada).