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