Both teams had already booked their place at the Rio de Janeiro Olympics in August by virtue of semi-final triumphs on Friday, the US blanking Trinidad and Tobago 5-0 and Canada beating Costa Rica 3-1.
But when it came to bragging rights for the North and Central America and the Caribbean (CONCACAF) region, the Americans were determined to complete an unbeaten run to the title on home soil at Houston, Texas.
Horan scored in the 53rd minute and Heath added an insurance goal in the 61st to give the reigning Women's World Cup champions the victory.
The Americans won the event for the fourth consecutive time, improving to 18-0 with one drawn in all-time Olympic qualifying matches.
The US women are the three-time defending Olympic champions and seek their fifth gold medal in six attempts at Rio, their only loss coming to Norway in the 2000 Sydney final.