The U.S. Open Cup released the future dates/times/locations for the upcoming rounds of the tournaments. If you look closely, you’ll see Seattle is scheduled to be the road team against the Kitsap/Portland winner.
Here’s the relevant bit from the release:
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Tuesday, June 29 — Seattle Sounders FC (MLS) at Kitsap Pumas (PDL), 7 p.m. PT
Bremerton Memorial Stadium; Bremerton, Wash.
Wednesday, June 30 — Seattle Sounders FC (MLS) at Portland Timbers (D2), 7 p.m. PT
PGE Park; Portland, Ore.