I have been told the 50 is extending, so it makes sense that less traffic is on the 148. I've mostly driven on the 148 when I used to participate in the Canadian Ski Marathon, so used to drive out to Papineauville, but its been maybe 7 or 8 years since I've done it.
I may ask you details one day of your route, I have family in Ottawa so may one day head out by bike.
Salut