Peel the guavas with a vegetable peeler. Cut them in half, crosswise and use a spoon to scoop out the center portions of the fruit to remove the seeds. Discard the seeds. Cut the guava into 1" -2" pieces.
In a large saucepan, combine the guava, sugar, water, vanilla seeds and vanilla bean as well as the cinnamon stick. Bring to a boil, then reduce heat and simmer on medium low for 15 minutes. Remove from heat and let the guava syrup steep for 20 minutes.
Place a large strainer over a large bowl and carefully pour the fruit and simple syrup into the strainer. Reserve fruit for another use.
Set a fine mesh strainer over a large jar and strain the remaining sediment from the simple syrup. Let the syrup come to room temperature and transfer it to a jar with a tight fitting lid. Refrigerate for up to 1 week.