Weather should be fine, although my previous suggestion about a Raincoat would probably be the most important thing. I doubt you'll see temps in the 80's, 90's that time of year. Most likely the temps will be in the low to mid 70's. The lowest I've seen it that time of year is in mid 50's.
I think the easiest way to explain this for ya is to look at what New York City or Boston weather is that time of year, then subtract about 5 degrees from the Temp and you'll have Halifax's weather pattern ;-))
Pack a Rain Coat, and a Sweater/light Jacket and you'll be fine for Halifax.