If you're looking for a more detailed, up to date look at Ontario's Highways, visit Scott Steeves website, Ontario Highways, as well as The King's Highway Ends, a photo documentary of the termini of Ontario's Highways.
... About one third of the WB traffic between Ottawa and Carleton Place on highway 7 turns SB on 15, another third stays in Carleton Place, and the final third
I believe you're correct with regard to I-81. I recall reading that the construction of I-81 north of Watertown, where even today volume/demand is low, was to
... I highly suspect that there was also a cost factor involved with 416. The 416 route is short - only 76 kilometers from 417 to 401. A 415 route would have