Sorry, new at this, actually posted from Alberta, Canada

Unless you really want to drive through Portland, get off I-5 at Kelso/Longworth and cross the Columbia River there and go west on US 30 to US 101 in Astoria.
Make a stop at the Tillamook cheese factory which also has great ice cream.
Continue south all the way to Reedsport. Spend a night in Reedsport. Take Rt. 38 east from Reedsport. About 5 miles east on 38 you have the chance to see Roosevelt Elk from a viewpoint. Take Rt. 138 south out of Elkton to get back on I-5.
Depending on the season of your trip I might suggest taking a short detour over to Crater Lake on your way to Lake Tahoe.
Were you planning on the scenic route east of Redding over through Susanville to get to Lake Tahoe?

With 3 days, you can drive the whole coast to
the redwoods, come back up 199 to GP, then zip down
to Ca 89 at Mt. Shasta and cut right over to Lake Tahoe.
I wouldn't miss the Southern Coast, if you only had to pick one.
You could come down 5 to 126 at Eugene and head West.
Personally, I'd skip the Ca border to Eureka part of the drive.

Let me expand on tomfuller's suggestion: Leave the freeway at exit 39 and go west on state route 4 to Cathlamet; catch the $3 (car, driver, and passenger total) ferry across the river to the Oregon side, continue on US-30 to Astoria and then turn south on 101 to drive the length of the Oregon coast. The ferry ride is cheap, it is much more scenic than taking the bridge to US-30 at Longview, and it is a nice break in a day of driving.

I was just in Oregon last month. The friends I visited said the southern coast is the most scenic portion. We drove the coast between the California border and Bandon and it was beautiful (actually started by driving down I-5 to Grants Pass, over US 199 to near Crescent City, CA, to see the redwoods, and then north on US 101).

So if you can fit in seeing redwoods around Crescent City, I encourage you to do that as well.

The day we did the coast trip we had perfect weather. My friends told me that sometimes it can be so foggy or rainy that you can hardly see anything, so be aware/prepared.

Thanks for all the good advice!

I am partial to both the Northern coast and the Southern Coast. It takes some time to navigate HWY 101 and not all of it is an exciting view of the ocean. If you decide on visiting the northern coast, I would recommend Cannon Beach. It has lovely little shops, good food, and a great beach. If you plan to stay overnight I would highly recommend the Surfsand Resort. I have stayed there several times and it is fabulous! If you like coffee you have to visit the Sleepy Monk coffeehouse. Absolutely the best coffee! And if you like Brighton jewelry Cannon Beach Leather has a wonderful collection. For an affordable lunch and /or dinner I would recommend Fultanos pizza. I never order pizza but they have great sandwiches and the taco salad is awesome. Cannon Beach is also close to Seaside which is a touristy town, great beach and little shops. One restaurant we love to eat at in Cannon Beach and in Seaside is Doogers. Great fish tacos. If decide to hit Southern Oregon I would recommend Bandon. A fun little town, face rock is at the beach and I the wild animal park is a fun experience. Sort of a walk through Wild Life Safari. The entire OR coast has something different to offer, I hope you find what your looking for. Happy Travels.

My favorite view place is just south of Lincoln City - at Depot Bay - where from the Surfrider resort (reasonably priced) - you might see some whales, and they have a good restaruant. http://surfriderresort.com/

I like the rugged part of the Oregon Coast - more of the Northern half - but the sand dunes down by Bandon are also pretty.

The best ocean views from Highway 101 are just south of Cannon Beach, between Yachats and Florence, and between Port Orford and Brookings. The drive from Brookings to Eureka is also spectacular because it offers redwoods as well as ocean vistas.

Highway 299 from the coast to Redding is also very scenic.

Portland-Cannon Beach-Brookings-McKinleyville (Eureka)-Redding is 631 miles and 14 hours; Portland-Yachats (via I-5)-Brookings-McKinleyville-Redding is 573 miles and 12 hours.

HTtY

Personally, I'd skip the Ca border to Eureka part of the drive.

I couldn't disagree more. We have made this drive many times (including north to south and south to north on a road trip from Seattle to California earlier this month), and we enjoy it every time.