Depends on the time of year, but $5-600 for a direct flight on AC is pretty decent. I've definitely paid much more to fly that route during a holiday week.
AC also has a monopoly on non stop YYZ-LIM and does not run the route that frequently so capacity is limited so prices can go up quickly. If price is your main concern, AA/LATAM is usually cheaper, but it will involve a layover, and sometimes a long one in Miami.