Both types of darner have a notch in their front stripe as well as a rearward extension extending back from the top. The difference between the two is the angle of the notch on the front stripe. If the notch is deep, greater then 90 degree then it is a Canada darner, if the notch is shallow, less then 90 degrees then it is a green striped. The back stripe of both types is not notched at all. You can see the notch on these is pretty deep so I would guess that these are Canada darners. I photographed them at the Carpenter Nature Center in September. The second photo is an excellent example of a wheel, which is how dragons mate. They can actually fly pretty well even when they are locked together like this.