In order to travel from Dallas to Seattle by rail, you will have to catch a connecting train in Chicago, as there is no direct service between Texas and Washington. This appears to be one of the only options if you wish to take an Amtrak train from Washington state to Dallas, as the only other possibility would be to travel to San Antonio, make a connection to Los Angeles and then transfer again onto a Seattle-bound train. I would recommend that you check out Amtrak's national route map by clicking here.