A little past the summit there is Manning Park Lodge where you can get something to eat and buy some groceries (not a great selection). You can stay at the lodge or one of the campsites in the park if you want to take this slowly. Energetic types carry on to Princeton. However between the park and Princeton there is one more significant climb, Sunday Summit.
From the Lodge you once again lose some elevation, this time about 750 ft over 10 miles before the climb to the summit begins. This again is fairly steep but not too long; about 950ft over 4.25 miles. After the summit there are a couple of little hills and then downhill to Princeton, which has motels, campgrounds and groceries. These are three pretty short days. 13, 29 and 42 miles. When I did a cross Canada ride I divided the climbing this way over three days but I tacked the first day's climb on to the end of a ride from Chilliwack and on the third day I went well past Princeton.
From Princeton to Tonasket, through the Nighthawk border crossing, it is a relatively easy ride of 90 miles and about 1300 ft total elevation made up mostly of rollers. This route gets you past Rainy, Washington and Loup Loup passes but of course does not get around the next passes on the route. The two main benefits are less climbing, about 2200ft, and no long gaps between places with at least basic facilities. However you will probably add some mileage to your ride depending on where you start.