There's a reason why Hood River is the wind surfing capital of the U.S.
I can recall fighting the headwind in my granny gear and cursing the fates.
And it's an equal-opportunity wind on both sides of the border.

If you are not opposed to going off route and bypassing Portland metro -
You can head north to Goldendale on US 97 - then Glenwood Road (paved) -
Then Forest Road 23 north from Trout Lake and FR 90 (both paved) west to Hwy 503.
Where FR 23 and 90 meet you are not far from spectacular Takhlakh Lake. (gravel)

Another option from the Tri-Cities is to follow the Yakima Valley to Yakima -
Then take the lovely US 12 route over White Pass and the Old Pacific Hwy to Longview.

West of I-5 - - I agree with the arguments in favor of the Washington side.
Cathlamet is a charming town on the Columbia -
The wildlife refuge has a paved back road along the river - - super!
And camping at Skamokawa is simply the finest.

Ending your trip at Cape Disappointment is no disappointment.
Cliffs, lighthouses, a nice little swimming cove between the rocks.
Fort Stevens is O.K., but just O.K.

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I've ridden both sides of the river a number of times.
Hwy 14 on the Wash side is pretty remote west of I-82, light to mod traffic.
I-84 on the Ore side has good shoulders, but interstate traffic - safe but annoying.
Hwy 14 west of the Dalles really starts to get bad traffic and has limited shoulders.
The Old Columbia River Hwy and its connecting trails is super - waterfalls and Vista House.
Traffic is light except on weekends when it is a popular outing - plus a lot of climbing.

Check the wind forecast and if its really bad consider US 12 via Yakima.
There are back roads all the way to Naches and the stretch around Rimrock is lovely.
Open views, trees, mountains, river, lake - plus plenty of camping.

Safe trip - - J