Another vote for Gardyloo's drive down the coast plan on the pre-wedding day.

If you want to do the gorge, one option would be to take Hwy 34 from the coast to Corvallis, head up I-5, then do a part of the fruit loop from south to north, then take I-84 directly to PDX. You could stop at some fruit stands along the way, and grab a bite in Hood River.

Yep, it's mostly windshield time, but you'll get an array of different scenery that way, and some local produce.

If you wanted less driving and more time out of the car, you could head up the coast further before crossing on Hwy 18 north of Lincoln City, have some food and wine tasting in the Dundee area, then do things east of Portland before looping back around to the airport.

It sorta depends on how you want to maximize your time during that day.