Things to consider: there is no Sightseer Lounge Car on the SEA section (#7/#8)and No Diner on the PDX- SPK section.
Thus you can have Dinner in the Diner between SEA and SPK, see Puget Sound and the Cascades up to the Cascades Tunnel in Daylight during the Daylight Saving Time period.
Then from SPK-PDX on #27, you will be given a Boxed Breakfast,if in a Sleeper, ( OK but not as good as the Boxed Dinner PDX-SPK on #28 ) and roll down the Columbia as the Sun comes up!
If I was going, I'd take a Cascades train PDX-SEA, ( early,)do #8 SEA-SPK, then #27 SPK-PDX.