A couple years ago, some friends and I did a very-small-group ride from Seattle, up the Burke Gilman Trail to Blythe Park in Bothell, then south on the the Sammamish River Trail, down the eastern side of Lake Sam, and into Issy, where we took some back roads to the I-90 Trail and returned home through downtown Seattle.
We wound up on the 'regular' roads once the BGT ended in Blythe Park, although this was short, and more through Redmond - this part was a bit harder to find. Those were the two points that were slightly confusing, although none of us had cue sheets or a map, just vague memories of having worked somewhere in the ballpark. It wound up being almost exactly 100 K / 63 miles, from Eastlake. If it's useful, I can probably find and send you a gpx file.
There's a detour on the Burke Gilman Trial right now, and you'll hit it on this ride. It adds a few miles.