A quick zip up to the Gaspe could be done in a week, but it is a mixed bag of roads and traffic. It's a little harder to find interesting back roads, and you might get stuck behind a Winnebago...
Cape Breton is the scenic Nirvana (prejudice showing here...), but it's a bastard trying to do it justice in a week counting the 'in-transit' time. You can see enough in three days to want to come back. First time I did it in two and missed a ton of stuff.
Of course like most trips, you're screwed if it rains!
Fall is the best riding weather. Crowds are gone and the leaves may be changing. It stays warmer than the mainland because of the ocean temperatures...
Best road in is highway 4 (104) because it has almost all been rebuild now.
Irish Cove Lookout by
designthreedimension, on Flickr
Side roads around the Bras d'Or lakes are spectacular and not that hard to find.
Bras d'Or Lakes drive near Roberta by
designthreedimension, on Flickr
as a matter of fact, there are sideroads everywhere (this is near the 'Fleur de Lys' trail on the east coast) that are worth looking for...
Riding early in the spring is uhh.... 'bracing' when sea ice is still around in April... (Brrrr....)
Ask Google for 'Cape Breton Bikefest 2010' and check out all the info from the results!
