There are several airlines that will get you to Halifax, Nova Scotia, and airlines often have more frequent flights in the summer months.

I often use Expedia to try and see what's available

Expedia.com

There are several airlines that will get you to Halifax, Nova Scotia, from within Canada including discount airlines. Often Direct or Non-Stop depending on your departure city.

Air Canada

Porter

Flair Airlines

Westjet

The following airlines have direct flights to Halifax. Where direct flights aren't available, it's most common for routes to arrive in Halifax via Toronto, ON; Vancouver, BC; Calgary, AB; or Montreal, QC.

Condor

Lufthansa

Iceland Air