I bought the new version of SeaClear from www.cruisingservices.net - it came bundled with all US Charts on a DVD. Well, lets say - all the charts I've needed so far. For a small additional fee, they included a CD with the charts for Eastern Canada. Recommend you check them out. Can't beat it for the price!
As for using a PC as a chart plotter, it has it's obvious disadvantages. The screen is not viewable in sunlight, it's not waterproof, it's difficult to mount where you want it, and it has a clutter of cables for power and the GPS signal. But it does work, and is wonderful for planning purposes. A printer (check out the 12V Canon BJ-10ex) allows you to print out a hard copy for the immediate future use.