You're missing my point. The mini and flex are basically taking the (E/i)-TTL information flowing between the camera and the flash (through the hotshoe) and duplicating it across the radio link. Since Nikon cameras and flashes speak an entirely different language (through the different hotshoe pins) than Canon cameras and flashes, there is absolutely no way for them to talk to each other. Maybe theoretically, through a translator device, but nobody has invented such a thing.
Edit: Maybe you're saying you hypothetically were to have a Nikon-specific Flex and a Canon-specific Mini. It still won't work, except in the basic manual Pocketwizard channels (ie. the Plus2 compatible channels) that both should support.
It's like talking on a walkie-talkie to someone who speaks Chinese. You still have to know Chinese to talk to them, even though it's over a radio. An oversimplification, yes, but it's demonstrates my point.