They use estimated processing times that are posted on the USCIS website, so to me it makes more sense to just look up estimated processing times yourself (which is free).
It depends on the airport and your travel arrangements. If you have a layover at a Canadian airport before flying into the US, you may be able to clear immigrations in Canada. If you plan to land in Canada and drive across the border, your port of entry will be at the land crossing so you will go through immigrations there.
You can not book the exact same travel itinerary as your fiance, because you will be a no-show for the first part of his travel, so they would cancel your return flight. He will need to book his travel, and as soon as he has the flight details for his flight back to the US, you book the same flight for yourself. You will probably need to book a round trip as if you are planning to fly back to Europe in a few weeks/months (because this is much cheaper than booking a one-way flight), and once you are in the US you can cancel that return flight.