I can not help you with travel conditions in that area but if you are planning on going to Louisbourg then your best harbour is the Port of Sydney. Use Sydney as a base to rent a car and travel to Louisbourg, it will take approx. 1 ˝ hrs to get there. Keep the car(s) for two days because you will want to drive the Cabot Trail Loop on the North tip of Cape Breton. This is a 185 mile round trip loop on the edge of the ocean that some feel is in the top 10 drives of the world (ok, maybe they are Canadian too).
Halifax is a great city to see in summer and if you have the time while there it is worth it to take a short half day trip into Peggy’s Cove, a small fishing village built up on a very rocky terrain. http://www.portofsydney.ca/index.php?menu=2&p=2.2 http://www.cabottrail.com/ http://www.peggyscove.ca/
Hope this helps