Seattle's matches are against Vancouver Whitecaps FC on Feb. 3, and against the Portland Timbers on Feb. 6 at Kino Sports Complex in Tucson. While the Sounders' matches are part of the event, they're considered friendlies that won't be part of the actual cup competition, which is being held a couple weeks later.
In addition to the three Cascadia clubs, MLS is also being represented at the event by Sporting Kansas City, Houston Dynamo, San Jose Earthquakes, New England Revolution, Real Salt Lake, and Colorado Rapids.
The Sounders have participated in FC Tucson's tournament for the past three years, taking first place in 2013. Tucson was formed in 2010 as part of the USL's Premier Development League, and have been organizing the Desert Diamond Cup since 2011.
The Sounders are expected to announce the rest of their preseason dates, as well as the exact details of February's CONCACAF Champions League quarterfinal meetings with Club America, in the near future.