Originally posted by Andy Fern attracted to its video capabilities
If video is the focus then Canon is likely a better choice.
Originally posted by Andy Fern I expect the AF is probably somewhere ahead
AF on the k-3 and k-3II (I assume that is what you are comparing to) is just about flawless. Really superb. Tracking however is not as good as other brands, partly because the lenses cannot keep up, partly because Pentax tracking implementation is not as sophisticated. If the interest is in tracking, best to look elsewhere. For AF alone though, it just does not get any better than the K-3.
Originally posted by Andy Fern what is the build quality like
I've not personally handled the 80d, or the 70d for that matter but I've always found Canon build to be rather cheap feeling compared to Pentax. But I suspect that is only subjective, the camera is not going to fall apart or anything.
Bottom line, there will be no detectable difference in image quality so look at the feature set and pick the camera that best suits. Agonizing over the gear is a waste of good shooting time.