I agree with New Moon: grab a Waggoners and have a good look at it. Then start to narrow down what you want to do.
Essentially from
Washington to Campbell River,
marinas and resupply is plentiful (diminishing in regularity as you
head north). Campbell River to the N. end of Vancouver Island is sparser with Port MacNeill as the main resupply. The outside of Vancouver Island is all small villages and wild and beautiful
anchorages. North of Vancouver Island you have Shearwater, which is small and Prince Rupert which is pretty big and that is pretty much it. And there is Haida Gwaii
offshore for even more beautiful and rugged landscapes.
To sum up, the further north (or west) you go the less facilities available and the more beautiful the scenery