After much research it was determined that you can NOT use Authorize.net for credit card processing in Canada. They will only bill in US funds and will bill the same amount in US funds as what the Canadian cost is on the registration item being sold.
That means that a $100 CDN funds course would be billed at the current conversion rate which could be anywhere from 5 - 20% depending on the world economy!
In addition, there may be US dollar premiums that the user may have to pay for making the purchase (as advised by Authorize.net).
One of the largest credit card processors in Canada, with lots of API information available for developing interfaces, is Moneris.
http://www.moneris.com/
It would REALLY help us Canadian users that don't want to deal with PayPal fees or force users to call in their credit card numbers if an interface to this processors could be provided. We have a great discount fee negotiated with the banks and using PayPal just doesn't make business sense.
Would be willing to help in anyway we can