Having seen far too many busted-up boats along the highways I firmly secure my canoe when traveling. Not only to the rack but also to the vehicle frame, both for and aft. Remember that a reversed canoe will cup the wind giving far more lift than a kayak.
As to PFD, none that I've encountered are comfortable in every scenerio. And the sospender type works best on the display shelf where, in my estimation, it should stay. I'm sure steelheader69 could give you the best on this.
I rolled my canoe two years ago in the river with my 13 year-old son along for the ride. Although it seemed to have happened in slow-mo there wouldn't have been enough time to activate an inflatable PFD's manual mechanism and I have little to no faith in the automatic operation (think airbag). No, the old-fashioned foam type III did just swell.