There are several routes you could take to Astoria from Portland. If you take Highway 30, there aren’t too many tourist destinations, but there are a few viewpoints over the Columbia River. Highway 26 is another option, and along that route you’ll find various viewpoints and parks that are worth visiting, also places like Camp 18, which is a strange but delightful restaurant/logging museum. And you can’t miss it – it’s right on the highway.
If you take Highway 6 to the coast to Tillamook, you should visit the Tillamook Cheese Factory! And then proceed up Highway 101 to Astoria. On 101 you’ll find lots of parks and towns that are worth visiting.