Well some 18 months have passed since the previous poster's woes with this and just a quick update to let anyone in a similar situation know that nothing seems to have changed..
1) Went to the Etihad website "Book Chauffeur" page and entered my booking ref and UK address. All appeared to go smoothly and no error messages
2) A couple of weeks passed and I vaguely remembered that I was expecting a confirmation email. Nothing received so eventually I called the Etihad call centre here in Singapore to check that everything was ok and was then told the booking was rejected due to no matching ticket number. Was told I needed Air Canada to request this as ticket was issued on their stock. Protested that AC wouldnt have a clue about this but she insisted I need to follow this procedure.
3) Called Air Canada. They didnt have a clue...
4) Called back Etihad. She said she would call Air Canada.
5) Etihad called me back. Told I needed to call Air Canada in Canada not Singapore
6) Called Air Canada in Canada. They didnt have a clue...
7) Called back Etihad. She said she would call Air Canada.
8) Etihad called me back. Told me I needed to call back Air Canada after 0600 ET when the "resource desk" would be open
9) Called back Air Canada. Told Etihad had already contacted them but they needed a UK phone number. gave them the phone number (Which was in my original booking on the Etihad website anyway)
10) Etihad called me back. Booking confirmed.....
So fingers crossed.. But surely there's got to be an easier way...