In Canada I would not use the "avoid Hwy's" feature. This tends to send cyclists on wildly circuitous routes that can add hundreds of Km's of sketchy roads with little or no shoulders in order to avoid safe roads with good shoulders. A perfect example is Hope to Revelstoke. Avoid Hwy's sends you up either the Fraser Canyon or the Crowsnest (both of which are Hwy's) and which have worse shoulders than the Coquihalla and adds at least 100km's to the route.

I use google to select a basic route and then the street view feature a lot to actually see what it looks like. I know I can ride about 100km/day pretty easily so I use that as a rough guide when looking for camping areas, stores etc... The good thing about the bike feature is that it shows rough elevation so you can plan distances accordingly.

I tend to look at web reviews/suggestions with a jaded eye. When I was looking at a cross country route from Winnipeg to Vancouver the common suggestion was west to east and took a crazy zigzag route north of Calgary east that made no sense what so ever. West-East is suggested due to prevailing wind but I found it didn't matter except near the foothills while westward also gives huge uphill climbs right off the bat compared to East-West.

Several websites suggested the same route and I soon realized that most had just copied each other and regurgitated it.