Originally Posted by jlemon

26. (2001) Starting this morning from Tijuana International Airport just south of the U.S. Mexico border, you’ll somehow make it all the way up to Yellowknife, NT before the day is done. For the record, Yellowknife is way up in the Northwest Territory of Canada.

Rather amazingly, only three nonstop flights will be required – each aboard a different airline. Three different aircraft types will also be involved, with two of them having been built by the same manufacturer. So then, you know the drill by now. Please provide us with all the relevant details.

Well, I believe that Tijuana (a suburb of San Diego) never had much in the way of transborder service to the U.S.
However, I do recall one Mexican air carrier that did provide such service: Aero California. So lets board one of their DC-9-30 aircraft and make a nonstop hop up to LAX.
And once in Los Angeles, we'll board an Air Canada 767-200 and fly nonstop to Edmonton International.
We'll then connect to a 737-200 operated by Canadian North and fly nonstop to Yellowknife

Well, I believe you're right about the dearth of trans-border flights north of Tijuana. And I do remember Aero California running a DC-9 of some variant up to LAX. Unfortunately, that flight is not reflected in the OAG used to reference this question. We're looking for a different airline operating a different as yet unidentified aircraft.

No DC-9s nor 767s of any variant were involved in this itinerary

Air Canada is Correct! between Los Angeles and Edmonton. However, the aircraft was not a 767

Canadian North is Correct! between Edmonton and Yellowknife. However, the aircraft is not a 737-200. It is an as yet unidentified aircraft

However, a 737-200 is involved in this routing.

So armed with this veritable cornucopia of clues, I expect your next guess will be much closer to our protagonist's routing

Please, guess again!