Peter, you still have those suggestions that I emailed you a couple of years ago?
Like you said, one of the challenges in exploring new fisheries is not knowing the timing and size of the run. In the Lower Mainland, the Chilliwack River certainly excels other watersheds when it comes to the quantity of returning fish each year, but the quality of the fishing does not necessarily fit visiting anglers' expectations.
One tactic that you should considering is to take a look at the pre-season salmon forecast for each watershed by Fisheries and Oceans Canada. If you go to the following page:
http://www.pac.dfo-mpo.gc.ca/fm-gp/species-especes/salmon-saumon/index-eng.htmScroll down and currently you'll see "Pacific Salmon Stock Outlook 2009". If you click on it (you may need to create an account to see the page), you will see the rating of predicted returns of each salmon species from every watershed. 4 being the best expected return, 1 being the lowest expected return. When 2010's stock outlook is released (sometimes early next year), read through it, pick out a few rivers that may catch your attention based on the ratings. Do a search on these rivers, you'd be surprised by the amount of information that you can gather through these steps.
After that, if you still need more information, you can always post up questions on specific watershed once you finalize when you will be in Canada, others maybe more helpful when those details are given.
god jul!