I think Canada has the same chances of earning the 0.5 spot via the 7-35 route or the hexagonal route, and here is why.
My thoughts on each Teams odds of finishing fourth in the hex. (If Canada was included in the hex.)
Costa Rica 30%
Now Canada's odds-on progressing Through 7-35 route:
Group stage: 90%
Round of 8 (potentially a team like Curacao) 70%
Round of 4 (potentially a team like T and T) 55%
Round of 2 ( team like Panama) 40%
0.9 x 0.7 x 0.55 x 0.4 = 0.14 (14%)
More or less the same odds.
The problem I have is that being involved in the 7 to 35 route, leaves no possibility of automatic qualification to the World Cup.
What I would do to address this, is have the winner of the 7 to 35 stage play the 3 and 4 finishers of the hex in a modified home and away group of 3 to determine the automatic World Cup spot and the .5 five spot.
The modification would be that the 3 and 4 finishers from the hex, would not actually play each other at this stage (because they already have). Their points against each other would carry over. So the 7-35 champ would play the 3rd-place hex finisher home and away and then play the 4th Place finisher home and away.
The first place finisher of this group of three gets the automatic spot, the second-place finisher gets the .5 spot
It would only add two extra games beyond what has officially being proposed, and in my opinion is a more fair option for the 7-35 teams.