We drove to NS 20+ years ago. My recommendation would be do do as we did and take the ferry over to Yarmouth from Portland, ME. From Yarmouth, we headed SE towards Halifax, then worked our way east and up towards Bay of Fundy, then worked our way west toward and thru New Brunswick and back in to the USA from there. We didn't make it up to the Cape Breton area on that trip but hoping to include that area, to include Sydney and especially the Cape Breton Nat'l Park (have heard of great campgrounds there) in our next trip up there, around August of this year. To see and really enjoy all NS has to offer, we're planning to spend a month to 6 weeks there on our next trip. Enjoy!
PS: Canadian boarder and customs authorities take a dim view of firearms and other 'contraband', so be sure you don't have any on board your RV, which is subject to a thorough search, if they so desire. So, don't have anything on board that might be deemed 'contraband'. I don't have any personal experience with this issue but have hard horror stories from some who have.