Finally got this to work by the most strange route and a tip from a Canon engineer who came and reflashed the firmware / flushed the print queues and did general full reset on it...
Generic Postscript should work...
Mac has 3 possible ways of printing once you've selected the way you want to connect - IPP, PDD or HP Jetdirect - now which one of those do you think worked once we selected IP connection and plugged the IP address in....
IPP, PDD - you'd be wrong, HP Jetdirect worked with a generic post script, odd but true....