I'd get the Tokina over the Canon, too - but it's a little letdown that the mk2 version for Canon seems to be not even face-lifted, but just with new coating.
Whilst the benefits of a better coating should never be underestimated (more of the wrong light reflected away, more of the good light let through) the positive side is that the cheaper mk1 remains excellent value..
I actually had a bit of bother getting hold of one, and so can only imagine that the used value, should I ever part with it, should be a good proportion of it's new value.
I'd get the Tokina over the Canon, too - but it's a little letdown that the mk2 version for Canon seems to be not even face-lifted, but just with new coating.
If you rent it, please let us know your findings - I'd be very interested since you seem to be very specific about the lenses you use. But everything I've read about the Tokina is very favorable (it's nearly a prime lens with the tiny zoom range), it's f2.8, it's very sharp and while Canon might be better the little distortion is simple to correct in post.