What sort of a trip are you thinking about? Hopping from one harbor to another in one day? Or are you thinking of a multiday trip?
For a daysail coming up in the next couple of days, you can look at forecasts for wind and current and tide and use that to plan a route on something like Google Maps (I've used the Geogarage one too, and I find Google Maps to be a bit faster, plus you can save your routes). I will sometimes make zig-zag courses for legs I know to be upwind, or I'll leave it straight and multiply the time by 1.5.
You can do the same thing for a sail that's a couple of days long, but you should plan several routes in case the forecast turns out wrong. It helps to know the sailing area well.
If you're just dreaming, "Man, I'd love to sail to Hawai'i... wonder how long that would take?" You can do the same thing. Again it helps to know the weather patterns. Plan a route that keeps the wind on your quarter (often faster than a great circle route), and assume 100 nm per day (which you can modify depending on your boat, but that's a decent conservative estimate).
edit: sorry, guess I didn't fully read your post. I suspect river sailing might throw a wrench into the works. Are you thinking about sailing to the St. Laurence and then down the coast? Or what?
s/v Laelia - 1978 Pearson 365 ketch
s/v Essorant - 1972 Catalina 27
Last edited by AdamLein; 05-12-2010 at 12:43 AM.