With my iMac 27” i5 I’m able to directly import full HD (1080p) footage from my 5D Mark II into iMovie. Not sure why you can’t… could it be a NTSC/PAL thing?
If you don’t figure out why, MPEG Streamclip should do the trick for you. You could also try and ask the guys in the cinema5d-forum, they know all about this stuff.