Up the coast. Take your time. Stop at Kalaloch Lodge if nothing else, but places like Moclips are cool at the beach as well. If wanting to see brand new; Seabeck
Continue on around the peninsula, a side trip to Cape Flattery (if the reservation is open) - maybe a side trip by Port Angeles up to Hurricane Ridge (might need chains - or at least have them in vehicle, but if a sunny day, road should by clear and dry). Onwards to Sequim (a cool animal park you can drive through), then to Port Townsend. A beautiful historic town on the water. Walkable. Fort Worden State Park just north of downtown. Then take the ferry from there to Coupeville on Whidbey Island. Wrong direction but I would backtrack slightly to Langley and stop to visit/walk/drink/eat. Then back up the spine of Whidbey Island to Deception Pass Bridge. After that Anacortes. Go from Anacortes up via Edison (good food) and Bow to Chuckanut Drive. Take it all the way into Bellingham. Hang in Bellingham before continuing north. White Rock just across the border has a beautiful boardwalk along the bay. Vancouver and surrounding area can easily be two weeks. Or drive from Bellingham into the mountains and up to Mt Baker (long one way though and can be crappy last miles up if snow).

This trip combines the WA coast with BC (near Vancouver) mountains and is pretty straight due north.

If having time and you’d like to see the Cascades and more, can drive east from Portland (along the Columbia or up via Mt Hood and then down to Hood River), cross the Columbia River (many locations) then take US-97 up towards Yakima (Palm Springs of WA). Continue from there up to Wenatchee. There either take US-2 west towards Leavenworth (fake German town, beautiful around Xmas and winters), Steven’s Pass (chains likely required to carry) and I-5 (for a beeline to BC). Or you can continue north on US-97, Chelan (vacation paradise in summer and shoulder seasons), Omak, Conconully, into the BC Okanagan (Osoyos, sunniest spot in Canada) and take the Crows Nest Highway (3) towards Hope and Vancouver. Or go north to Kelowna through the wine districts. From there you can head west and loop back towards Vancouver, further west towards Merritt and Lillooet to approach Whistler from the north and then onto Vancouver. Etc.

All a matter of time, what you want to see, weather, desire to carry chains or not, etc. Unless in a real rush, I would avoid taking I-5 up from Portland to Vancouver. Just a busy freeway with not many views - although coming into Seattle and seeing the skyline is cool.