The Snake River gorge at Twin Falls is nice. There are views from mall parking lots on by the highway bridge of the river. There is a drive down into the gorge, but you probably don't want to take the trailer down.
Other than that I84 stays out in the open, with lots of irrigated farm land in the west.
Irrigation water around Boise and Ontario comes from Lake Owyhee, a reservoir created by a early version of the Hoover Dam. There's a nice state park and campground on the lake. Can be windy and sunny. Also a bit of a drive off the the main highway. Farewell Bend is closer to the Interstate.
After Ontario I84 climbs into low mountains, and doesn't exit until Cabbage Hill and Pendelton.
US20 and 26 are alternative routes across Oregon that have been discussed numerous times. Dito for routes across the Oregon Cascades.