For your planning here is a good one. It will show you what you can and can't do :
A Better Routeplanner
For Fredericton, I can guarantee you, there is a Supercharger unless they pull it out of the ground.
As somebody mentioned before you can now drive from Montreal to Halifax on Superchargers only with a maximum strech with no superchargers of 238 km between Saint leonard NB to Lincoln NB.
Also from Fredericton, according to a better route planner, you can do Campbelton, either direct in Summer or with a stop in Saint Leonard during not ideal conditions
Miramichi, no problem of course !