I've heard the opposite, that it's really tough for Canadians to get internships in the US. Hopefully I'm wrong.
One thing to keep in mind is that soon APA-accredited universities in Canada won't be APA accredited anymore. They're all dropping it and sticking with CPA. Now, it SHOULDN'T be a problem (since CPA has tougher guidelines anyway) but that doesn't mean it won't throw some bugs in the system until they get it worked out.
As for getting accepted, I think they just throw everyone in the applicant pool and call it a day. I don't think it would help or hinder you.
Financially, tuition is pretty damn cheap. I pay $3000 a year regardless of how many courses I take. Assistantships are usually easy to find. I know at my school so many people are SSHRC funded that the school has to beg people to take assistantships.
Your US citizenship would probably "counteract" any negative impact the Canadian university would have on a US internship. I'm a Canadian going to a Canadian University but I still plan on applying to (mostly) US internships.
I know we've got one girl from Seattle in our program but I think that's the only American at the moment.