Are your flashes ones that can only be used, dedicated, on the Canon cameras, or are they ones that can be used as well either manually, or semi-automatically (i.e. you set the ASA/ISO on the flash, and read the aperture indication that corresponds to the distance range you need, then set that aperture on your camera)?

It has probably been more than 25 years since I sold these cameras (Canon A-1/AE-1p) so my memory on the subject is somewhat vague, but I seem to recall that these cameras did not offer any through the lens flash metering. As a result, they depended on the sensor on the flash to adjust the light being emitted by the flash.

If I am correct in my recollection, the only benefits of having a "dedicated" flash were that you were assured that you would not accidentally set a shutter speed that was too high for flash photography (faster than 1/60 second) and when you set the aperture on the flash (for the automatic range you had chosen), the cameras would automatically be set to that aperture. Setting the ASA (as it then was) on the camera may also have set the ASA on the flash too.

If your flashes are the semi-automatic ones, then it is merely a matter of using a generic cord to trigger the flash (I seem to recall that at least the AE1-P had a PC synch outlet), making sure that the settings on the camera match the flash, and taking care to make sure that the sensor on the flash is pointing at the subject of your photograph.