What does Canada-United States mean re cell phone calls.

Aaron, to subscribe to Fizz, your town must be in the territory of Fizz network (in green) on the map.
It's the only condition. And your total usage do not must get more 50 % in the partners-zone more than 3 months (outside the province of Quebec) .
If you have the plan, unlimited calls with coverage Canada/USA.
You can call and receive calls from everywhere in Canada and in USA.
They include your calls when you visiting too.

Aaron,
The most important rule , your calls in Canada and USA can be do on an occasionally base. No more than 50% of all your usage for 3 monthly consecutive. Fizz after, theses 3 months can stop your plan.

If you get the Canada-US plan, yes you can use it anywhere you are: Canada to US, US back to Canada. But as mentioned above, you can’t abuse this. Fizz says you can’t have more than 50 percent usage outside of the Fizz zone for more than three months in a row.
So for example, you live in Montreal and signed up for Canada+US plan. Spend two months in Florida every winter? Fine. Go the the US two weekends a month for business? Fine. Decide to live in upstate New York all year? not fine.
Staying put in Montreal (or anywhere else in the Fizz network territory)? Call any US or Canada number all day any day to your hearts content.