The fair place to meet is Oklahoma City, OK — the city closest to the midpoint of Miami and Portland. From the farther side that’s about 31 hr 8 min of driving.
Recommended midpoint
Oklahoma City, OK
From Miami
25 hr 43 min
1,226 mi to Oklahoma City
From Portland
31 hr 8 min
1,485 mi to Oklahoma City
Miami has the shorter trip; the split is off by about 5 hr 25 min. The alternatives below can even it out. Miami and Portland are about 2,705 miles apart.
Miami and Portland are about 2,705 miles apart by road. Split the difference and you arrive near Oklahoma City, the city closest to the halfway point between them. That puts roughly 25 hr 43 min of driving on the Miami side and 31 hr 8 min on the Portland 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. Oklahoma City still makes a fair, central place for Miami and Portland to converge, splitting the travel instead of asking one side to cross the country.
If Oklahoma City doesn't have what you're after, Albuquerque and Dallas are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Miami and Portland.
Oklahoma City, often shortened to OKC, is the capital and most populous city in the U.S. state of Oklahoma. It is the 21st-most populous U.S. city and 8th largest in the Southern United States, with a population of 681,054 at the 2020 census. Read more →
Miami is a coastal city in the U.S. state of Florida. It is the second-most populous city proper in Florida, with a population of 442,241 at the 2020 census. Read more →
Portland is the most populous city in the U.S. state of Oregon. Located in the Pacific Northwest at the confluence of the Willamette and Columbia rivers, it is the 28th-most populous city in the United States, sixth-most populous on the West Coast, and… Read more →
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.
Estimates use straight-line distance and typical road speeds; real drive times vary with route and traffic.