In summer the prevailing wind along the Nova Scotia coast is south westerly and although passing weather systems result in some variations, they don't seem to last long before the wind is again blowing from the SW. 

This means that if you are heading south towards Maine or New England you are likely to find yourself tacking the entire way. The tactic of waiting for a low to pass through and then setting off on the north westerlies  that follow it, doesn't really seem to work in Nova Scotia.

The other factor to be taken into account when passage planning is the sea breeze. The cold Labrador current flowing down the coast makes for extremely large temperature differentials between land and sea,  which in turn generates extremely strong see breezes. By mid afternoon on a clear day they can be blowing in excess of 25 knots and  seem to persist  much later in the day than one would normally expect, often  peaking shortly before sunset,  only to die away abruptly within 15 minutes or so of the sun setting. 

These breezes  also persist a remarkable distance inland. On a sunny day it is not uncommon to find the thermally accelerated wind actually increasing the further up a river or harbour entrance you go, so that by the time you come to drop anchor or go alongside you are in the strongest winds you have encountered all day. 

If day sailing southwards down the coast in fine weather, it pays to start early in the day and  to aim to reach your destination by early afternoon before the full force of the sea breeze against you kicks in. Likewise, it pays to tack offshore first thing in the morning when the gradient wind is blowing from the SW. When you see the sea breeze front forming along the shore line ( typically a few hours before midday) you can tack back inshore and as the sea breeze  fills in the wind will back to a more southerly direction lifting you up towards your destination.

An alternative strategy for those with plenty of time is to delay your journey southwards until early September when local sailors say it is not unusual to have prolonged periods of northerly winds.

Those heading northwards have little to worry about until reaching Chedabucto Bay and the Straits of Canso. The winds tend to funnel strongly down these straits from the NW leaving anyone heading northwards with a stiff beat in short uncomfortable seas.

Although the Straits of Canso offer the shortest route to the St Lawrence River, unless you specifically wish to visit Prince Edward  Island then the route through the Bras d'Or Lakes and round the north of Cape Breton Island is likely to be considerably more comfortable. Many yachts heading north eastwards from Nova Scotia to Newfoundland also seem to take the Bras D'Or Lakes route even though it is marginally longer than the offshore route.