Nearly impossible to get in Canada as fresh fruit, though nectar is availabe. But it's grown (and thus available fresh) in small amounts in the warmer southern states and certainly readily available in Mexico, the Caribbean, South America, tropical areas of sub-Saharan Africa, and some parts of Asia. High in vitamin C, some B vitamins, and calcium, and very low in Phosphorous.
http://nutritiondata.self.com/facts/fruits-and-fruit-juices/9793/2
http://www.buzzle.com/articles/guanabana-fruit.html
http://nutritiondata.self.com/facts/fruits-and-fruit-juices/9793/2
http://www.buzzle.com/articles/guanabana-fruit.html