Yes, you can. Most of the on-line mapping programs show rail routes once you zoom in far enough. Then you can switch to the aerial photo and, depending on the resolution for that area, you should be able to see the track.
Basically, just start in Seattle, zoom into King Street Station, then follow the track north toward Everett. The you should see a junction with tracks heading east. Just follow the tracks, look for the towns with stops, and off you go.
If I could make a suggestion, a really good topo map program that you can load on your computer is TopoUSA. This not only gives to the street locations, but various topographic features like streams, lakes, rivers, and elevation above sea level. I loaded it on my lap top and used it all the from Chicago to Emeryville except, of course, when we were sleeping. Without too much effort, I could follow the route from town to town and even predict the next curve, sidings, names of the grade crossing roads, and the names of all those little towns you just roll through. Then, to take the nerd factor to the ultimate, I used it on the flight home matching ground features to the map and knew exactly what I was looking at including, I might add, the rail lines. Worked great. I was entirely absorbed out and back.
My wife enjoyed it too. She said it kept me occupied so she could concentrate on her crosswords. She did, however, have a fear that I was going to haul the lap top down to the dining car and have the thing on the table as we ate dinner. I did not do that, but sadly I must confess I did consider the idea.
