Backpacker magazine has a quickie guide. I found this part about starting in Canada and heading south interesting.

A few hikers will begin in late June from Manning Provincial Park and hike southbound to Campo. Southbound hikers can still expect to average about 20 or more miles a day over 5-6 months. Those who favor this route will have a strong chance of encountering lots of snow in the North Cascades and should come prepared with an ice axe as well as plenty of insect repellent to contend with swarms of emerging black flies and mosquitoes across the southern half of Washington. On the plus side, the Sierra will be almost completely snow-free by the time hikers reach it around late September, plus they’ll enjoy a much greater degree of solitude and easier access to trail town amenities than thru-hikers traveling north to Manning.

You’d definitely have Washington and Oregon to yourself, and you’d hit the desert later in the year, when it might be a bit cooler. I’m surprised more people don’t do go southbound.