DC Fan wrote in post #5836702
An alternate strategy would be to use the flash as your main light, and use the sun as a hair light or a rim light from behind the subject. For that, you'd need only the Canon flash; have the camera and the flash facing toward the sun and discharge the flash on each exposure, using the flash to fill any shadow left by the sun's backlight. Pointing your subject away from the sun prevents having that person squint in bright sunlight. Using the flash as main illumination also can fill in the deep facial shadows that can result from midday sun. Canon's most recent E-TTL II flash system can work better for this than the older E-TTL and its inconsistencies.
Ahahahaha. As if E-TTL II doesn't have its own batch of awful inconsistencies?
Seriously, though, on-camera flash as your main light is going to be awfully flat and unflattering. Also, if you want to use decent length telephoto, which is ideal for portraiture, the flash might not be powerful enough for the distance.