Orlando and Seattle are about 2,546 miles apart by road. Split the difference and you arrive near Denver, the city closest to the halfway point between them. That puts roughly 32 hr 29 min of driving on the Orlando side and 21 hr 23 min on the Seattle side — the fairest single meeting point among the cities near the middle.
Over this distance most people will fly rather than drive the whole way. Denver still makes a fair, central place for Orlando and Seattle to converge, splitting the travel instead of asking one side to cross the country.
If Denver doesn't have what you're after, Oklahoma City and Albuquerque are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Orlando and Seattle.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.