Vancouver, BC - Las Vegas (West Coast down, ID back up)

[glc]

Day 1 - 400 miles. 7 hours plus stops and border delay.
Day 2 - 300 miles. 5.5 hours plus stops.
Day 3 - 500 miles. 9 hours plus stops. Best place to cross from I-5 to CA-99 is through Stockton on CA-4.
Day 4 - 300 miles. 5.5 hours plus stops.

Day 1 - 500 miles. 9+ hours plus stops. This is taking NV-318 from Ash Springs to US-6 to Ely. There are no services whatsoever on this route from Alamo to Ely. Taking US-93 through Caliente and Pioche is 50 miles longer.
Day 2 - 500 miles. 9 hours plus stops.
Day 3 - 250 miles. 4.5 hours plus stops and border delays.

I personally would see Shoshone Falls in the morning of Day 2, then only drive to Kennewick that night. Stop at Lake Easton for lunch instead of breakfast on Day 3. This will make the drive times 7 hours and 6.5 hours. If it's still early enough when you get to Kennewick, you can press on to Yakima - about 1.5 hours.