Some things to note about the stretch of roadway that is kind of along the Oregon Trail in Oregon.
The stretch through the Columbia River Gorge has changed many times. For one thing, the Oregon Trail didn’t pass thru there! A very winding two land road was built thru it in the early 1900s. This was replaced by a regular, river level road (US 30) later on. Parts of the old road remain open as a scenic highway. Interstate 84 (originally 80N) came later. Between the Interstate and the dams, the road got moved higher up.
After The Dalles, the Interstate follows the river quite closely for a long while. Which was also the route of US 30. But … thanks to dam building it’s been rerouted. The last major reroute was for the John Day Dam. They even moved the town of John Day!
But note that the Oregon Trail did not follow the river closely. It was well south of it. The area near the gorge is just too rough for wagon travel. Much easier 10 or more miles in.
Once I-84 leaves the river it cuts fairly straight across the plateau to the base of Cabbage Hill in the Blue Mountains. The Interstate passes near Pendleton, but not through it. Well away from the old highway.
The route up the mountain is quite different from the old highway. The two sides of the freeway are sometimes well separated.
Across the top of the mountains it usually follows or is close to the old highway. But many cuts are different, e.g., near where it comes out of the mountain near La Grande.
From La Grande to Baker to Farewell Bend the Interstate is quite different from the old highway in many places (especially in bypassing towns). But thanks to geography, it has to go thru the same narrow slots in canyons in many places. The widening of some of those canyons took quite a long time making this stretch one of the last ones of the original Interstate plan to be completed.
Note that near Baker, it passes a few miles west of the old Oregon Trail. From Baker south it takes a different route through the mountains for a bit.
Speaking of bypassed towns, north of Farewell Bend, the Interstate swings wide from the old RR center of Huntington. (Not named after the RR Huntington tycoon you are thinking of.) Really killed that town economically.
From Farewell Bend to Ontario things are quite different. The freeway cuts straight cross country over good sized hills. No previous highway or trail went that route. The old highway follows the Snake River. But it has been re-aligned several times. E.g., there’s a “bridge to nowhere” (over the Malheur) near the river. A short section of old pavement leads to one side of it. The rest was washed away. The highway was moved further from the river.
The Oregon Trail originally came into Oregon south of Ontario (and thus I-84 and US 30) and swung well west before heading to Farewell Bend.
If not restricted by passes, narrow cuts, etc., the chances of you being on the actual Oregon Trail while on I-84 in Oregon are quite small.