Well, there are a number of specific issues for places like Cannon Beach and Seaside in Oregon, and Long Beach in Washington.

Unlike, Socal, the coast of BC, Washington, Oregon, and the northernmost portion of California have a significant risk of locally generated tsunamis. If the Cascadia Subduction Zone generates a 9.0 earthquake, there would be as little as 15 minutes time before a huge tsunami struck. Some places, such as Long Beach, and Seaside have a significant distance to travel (on the order of a mile for Seaside, and several miles for Long Beach) before reaching safe ground. An earthquake that generates a major local tsunami would also do major damage, and destroy many roads, sidewalks, bridges, etc. Traveling a mile or more in 15 minutes over severely disrupted ground could be problematic for many people. And if it happened at night.......

Specifically with regards to Cannon Beach, for much of the town one must cross Ecola Creek, which is spanned by only two rather old bridges. In particular, the only practical escape route for students in the school is across one of those bridges. According to Sandi Doughton's book (mentioned up thread), that bridge is considered to be very unlikely to survive the earthquake.

You are correct that knowing the best routes to high ground is a good idea in any coastal area. However, some coastal areas are more dangerous than others, with a greater danger from tsunamis, and a longer route to escape.