Running near the Panama Canal from the Atlantic Ocean to Pacific Ocean is believed to be the fastest possible route to cross any continent on foot (The Suez Canal in Africa is over twice as long). The Trans-Continent FKT may follow any route across Panama as long as you start at one ocean and finish at the other. The only "rule" is that you must start/finish at a point that is clearly the sea/ocean and not an inlet body of water such as the Bahia las Minas (Bay of the Mines). It is not possible to follow the Panama Canal exactly but several road routes roughly parallel the canal miles to the east. Most routes will be between 45-50 miles and start/end in Panama City and Colon'.
There are no known speed attempts for crossing the country/continent but there is interesting history behind the crossing of Panama. The Panama Canal saved ships 8,000 miles of travel once it was completed and in 1928 Richard Halliburton swam the length of the canal. The Spanish conquistadors used a trade route they called "Camino Real" further east to trek stolen gold and goods to their ships. The US Army Ranger's previously had a jungle warfare school here and as part of their training the rangers would trek from Fort Sherman (Caribbean Sea) to Miraflores in Panama City (Pacific Ocean) in 2-3 days. There is no direct trail and any FKT attempt to complete the trans-continent in a day or less would require using mostly or all roads. It's up the runner to determine that safest possible route concerning local traffic and expressways.
Josh Sanders spent a few weeks researching and studying potential routes and the history so the route description should be very accurate. Help was provided by the US embassy.