Hey
Canhelp needs a Canadian co-borrower...but if you want to apply on your own signature they will accept that too, but you'll be eligible for less money. I just submitted the application so if you have more questions let me know. No need for a US co-signer though!
RBC has a line of credit upto 150 K for medical and dental students...they have a list of approved schools out of Canada, and from what I remember most of the US dental schools were on the list, but I would double check. I have the list if you want it.
I'm still researching, but so far I think it might be better to rely on canhelp first and the banks second, because you will have to make payments on interest while in school for the RBC line of credit, but with canhelp it will accrue without you making payments till after graduation.
Also lok into OSAP/federal canadian loans - they do give us some money and it helps!
Good luck!!!