I have to write a diary for my Social Studies class on what life as a loyalist was like. How long would it have taken them to sail from Boston to Nova Scotia, also known as British North America in about 1775?
Probably about 3 to 4 days, but less than 3 days would have been possible in very favourable conditions. However, one might have to wait several days for suitable sailing conditions.
This is a difficult question to answer as there are a lot of variables, not least type of ship, seamanship, cargo carried, wind speed and direction, and time of year.
That said, sailing speeds from around 1750 to 1780 averaged 4.5 to 5 knots, but in favourable winds it could be much faster. This would mean a sailing time of three and a half to four days, but 7 knots or more would have been feasible in very favourable conditions, thereby cutting the journey time to less than three days.
One actual voyage in March 1776 took 3 to 4 days. On the 17th of March, 1776, General Howe and the British evacuated Boston for Halifax, Nova Scotia, having had to wait for favourable winds. However, they did not actually set sail for Nova Scotia until the 27th of March, and they arrived at Halifax on the 30th of March. As Tomas By implies in his comment, some ships in this fleet would probably have been able to go faster.