I've only ridden from Portland/Vancouver to The Dalles, OR, which is 100 miles west of Umatilla. My preferred routing would be skip SR 14 on the Washington side and ride the south (Oregon) side of the Columbia River Gorge at least until The Dalles.
SR 14 on the Washington side has its moments, but it can be narrow and busy, with narrow shoulders and more truck traffic than you want. Plus there is about eight tunnels to pass through between Dallesport and Carson.
If you travel on the Oregon side, you will have to ride on Interstate 84 for at least two sections, which is unavoidable and legal. The two sections are from Yeon State Park to Bonneville, about three miles (until they finish the trail in this section), and fifteen miles from Wyeth to Hood River. But you'll be able to ride on sections of the Historic Columbia River Highway (HCRH), with its spectacular views and low traffic. And some sections of the HCRH are off-limits to cars, so you'll have some peaceful riding! Crown Point, Chanticleer Point/Women's Forum, Multnomah Falls, and the Mosier Tunnels are just a few of the scenic highlights of the Oregon side. There is some great views on SR 14 too, namely Cape Horn, but the HCRH has lots more.
After The Dalles, I have no experience, but heard SR 14 is a better option than the Oregon side (I-84.)
Crown Point and the Columbia Gorge from Women's Forum.
LHT avec Horsetail Falls.