Mine was sent to Detroit (via the Windsor dropbox). Got it back in 10 days with the visa stamped.
Yes, you can enter at any port. Flight, road or ship. Keep in mind, this is a one time entry after which you should not (ideally) leave the country (although you have officially landed) until you get your PR Card (60-65 days). Your PR Visa that is stamped in your PP that you sent to Seattle is valid for about 6 months, so plan your landing date properly (and chose off peak hours, like early morning, I landed at around 7.30am). Also, if you wish to go to your country of origin and return, you should do so, because you are exempt for duty on a number of items.