@wardy07. Ooh difficult one because they are so different. Okay, I don't have an M3 so can only comment on paper specs. However the EOS M which I do have (latest firmware obviously) produced great video for very little outlay. Remember the sensor is the same as the 650D which is no slouch at video recording.
So is it up to the job ? Yes of course it is but is the M3 better ? Well that depends on what you want and how much extra you are prepared to pay . The M 3s bonus points.....
Flip screen
Higher IQ from the 24mp sensor
Focus peaking
Optional EVF
Cons for video shooting
No mic socket for external audio recording ( although there may be a workaround )
How important are those to you ? This ultimately is what should be driving your decision.