Let say there won't be any offline-online workflow here, just to make things easier.
You can access XDCAM and Canon H264 files via AMA. In other words you can import them into Avid bins and work with them, but that won't run so good (especially H264). So after import you should make selection (clips, subclips, what ever) and transcode to Avid DNxHD MFX.
For DPX you will use Avid Metafuze. Free Avid application that runs on Win & Linux (no OS X). Metafuze will convert DPX sequences to AVID MXFs and keep the metadata
Edit with mxf files.
Export tiff sequence for Nuke
Bring back VFX sequence into Avid
Lock your edit
From here you have some different paths to CC suite:
A) Export EDL, purchase $500 MXF option for BM Davinci Resolve and conform Avid MFX files in Resolve
B) Export EDL, "bake" export your sequence, create cut list with EDL in Resolve
C) Reconnect original media ....
Again, I'm oversimplifying explanation here but I hope you'll get the picture how it works.
In Premiere you would import XDCAM, H264 and DPX original files and edit right away.
You can download trials for the both applications (you don't have to purchase via App Store just to try it out :) ) and test some workflows yourself.
