I have been looking at the Canon 60D and 7D, but after some deliberation still can't make up my mind.
I am in the same situation but also considering m43 on top of Canon SLR (I am a 7D user on land).
Sorry to add some more confusion but the 600D + Sea & Sea housing might also be an option to consider. Cheaper, works with fibre optic so if you have flashes like INON D2000/S2000 - my case- you can keep them at least to start with, and photos with 7D/60D/600D would be virtually identical.
And the 600D is smaller and lighter when travelling.