I have stats that show about a 50% match rate in the US with the NRMP for non-US IMGs. Stats specific from UQ, and independent of the UQ-O program, include an 83.3% NRMP match rate from 2016. The match rate here in Canada via CaRMS is ~65% for Australian trained Canadians, and approximately 73.6% for UQ. I have also been assured by the program director for UQ that any Canadian that has studied previously in Australia that wanted an internship has received one. The caveat here is that you cannot expect to be particular with your residency choices. That is to say that you cannot expect a plastics residency in Sydney if you're an international Australian trained graduate.
I would argue that the odds of being able to match into a residency/internship in any of Australia, Canada, or the US are relatively high, and thus any apparent crises for getting a residency/internship is inflated.
To answer your question, you must be concerned with state medical boards that place limitations on the number of weeks that can be spent abroad for either elective or core training blocks. Recognition by the California and New York medical boards will typically ensure that you can match and ultimately practice within the rest of the US provided that you complete your state board exams successfully.
Why is returning to Canada not an option or possibility here?