I'm puzzled by the Canadian accent sounding like British also, unless you mean a northeastern or New England accent (like Boston, which maybe sounds a little Irish to an untrained ear?). The similarity with British is more written and grammar than verbal.
Also, regarding why they teach American English in Latin America, I think it's really just because of proximity. English teachers in Latin America are more likely to have studied in the US when they're developing proficiency.
On the flipside, we're taught almost exclusively Latin American Spanish in the US (if you select Spanish as your foreign language), so while I get along great in Argentina, Peru and Puerto Rico, I sometimes have trouble being understood in Spain. And as hard as I've looked, it's nearly impossible to find (physical) classes that teach Castillan Spanish here.