Terrific area. Beautiful views, really can't go wrong. There is a lot of information at nwhikers.net regarding this area.
Here is a trail report of the Ross Lake to Whatcom Pass area.
The only issue you may encounter is that as you head west, the chance of significant rainfall increases. The PCT jogs a fair distance east as you approach the north of the state - if it were to truly follow the crest, it would likely take along the flanks of Mt. Baker (which in 1999 received in excess of 1,100 inches of snow).
So, if you are getting rain (or snow) on the PCT when you are in the North Cascades or Pasayten, on the west side of the cascade range they will be getting a lot more.
Just one thing to note, you are not allowed to hike from the Canadian side back into the U.S. - I didn't see anyone out there when I crossed the border a couple of years back, but up here they've reported a change in the rules and that they will be enforcing the rules. Just something to consider, should you hike the 8 or so miles from the border to the nearest lodge.
Again, I have no idea how they will enforce this, because I didn't see anyone out there, but perhaps something has changed.