Being based out of the center of the Maritimes (Moncton N.B) I can tell you that we have the same Diesel fuel that you use stateside, available at pretty much every gas station you'll see and much like the states not all stations are RV friendly to get in and out of. DEF is available in bottles at pretty much every gas station, walmart, Canadian tire and auto parts store along with every commercial truck stop.
Note that I drive a new Diesel pickup myself, no issues here. I actually find it harder to find DEF and Diesel in some areas of the Northeast USA than at home in some areas I've travelled to.
the only real difference you'll notice is that there's not much between cities so fuel up and stock up as you're often 35-60 minutes away from much of anything on some stretches of road.
Even though our season is much shorter than most of the US (May to October) RVing is huge out here, ton's of campers out on the roads and lots of spots to camp at.
Alex
