It is not a requirement to land in Halifax.
If you land in Toronto with NS nomination, and all your friends are in Toronto, and you don't have travel booked out of Toronto, and they go through your bags and find printouts of real estate listings in Toronto, and checking your email reveals conversations with companies in Toronto, then you'll be having a long chat with CBSA about your NS nomination.
If you're not landing in the province that sponsored you, you need to be able to demonstrate that you do intend to live in the province that sponsored you.