there is nothing to it really. a us citizen is free to "visit" Canada anytime they wish, having a PR application submitted doesn't change that. the important thing to remember is using the right language. Until PR is approved, a US citizen can NOT "move" or "live" in Canada, they can only visit. as a pr applicant it's usually best practice to be able to prove your ties to the US, in case the border agent asks. this doesn't always happen, though some people are pulled into secondary and are asked to prove a home/job in the US. generally, us citizens are allowed to visit for 6 months. How long they are allowed to stay per visit is up to the border agent. Once in Canada, the visitor can then apply to extend their stay within 30 days of the current visit ending. PR applicants are rarely denied extensions and it's common for people to request/get 12+ month extensions. As a visitor, the US applicant can NOT work in Canada for a Canadian employer. they have to wait until PR is approved, which is hovering around 6 months for US outland applicants.
you can't. all you can do is write a clear, concise application that leaves little question about the validity of your relationship. NY does not process family class applications anymore. Currently, if an interview is called, it WILL be in LA. there is no choice there. Whether the application gets shuffled to LA for an interview is in the hands of CIC and whether they think there is an "issue" with your application. Common "issues" that can trigger an interview are: non-accompanying dependant, relationship validity, criminal history, and the applicant being a resident of the us, not a citizen.
I would say about 99.9% of US applications are waived the interview, so if your case is straightforward, it really doesn't need to be a concern.
