I'm just putting my NZ CPL through the same process. Not sure about Canadian, but with Australian, if you have over 1500 hours you can (I believe) do the ATP theory and get a straight ATP licence. Otherwise you have to get a PPL based on your Aussie licence, then do the CPL theory test, Instrument theory test, then both practical test, after training through a flight school. The form to fill out is one of the first Forums in North america. I would suggest contacting a FSDO (find them under
www.faa.gov then bottom of the page click on "contact us"). They are generally pretty helpful and will be able to advise you if your Canadian licence can be transfered over easier.
Good Luck!!
Anita