I know the area well...
No matter how you look at it, you're a bit bottle necked to get from marysville to everett. You have only a couple options but none of them are all that great. Options:
1. Ride through marysville, take the flats over the sloughs, get on broadway in everett and tie in to the interurban trail. That will end up close to the everett mall and 128th area near I-5.
2. Ride through marysville, tie in to the centennial trail and then take lowell river road or cathcart way.
I live in the silver lake area and have ridden feom my house, through the snohomish valley, up the centennial, down getchel to Bob's burgers on 88th. That route was 24 miles one way. Option 1 would be about 16 miles but you're riding about 3 miles along a narrow, 55mph highway.
Honestly, if you could possibly incorporate a short bus ride from marysville into everett you would be saving yourself a ton of miles and/or keeping your personal safety on the road.
Hit me up with a pm if you ever want to ride.