Hey! great question. Unfortunately applying in the states is much harder. As another person mentioned above, its a much larger application pool and so while Canadian programs receive 200-400 applications, most of the good US schools receive 500 - 700 applications. The funding is also much more varied, but can be sometimes better. However, its overall much more competitive. I know several people who got accepted to 1-2 Canadian schools and got, maybe, interviews at US schools but no one got acceptances at US schools. I would say many of the applicants who get offers at US schools have at minimum 1 published first author paper, and several (2-3) years working as a post-bacc/research coordinator.
In my experience this has been accurate. I got interviews at 2 US schools and haven't heard back yet, but have already gotten acceptances at 2 Canadian schools. Its also worth noting that if you're a Canadian, you can always apply to tri-council funding opportunities, but if your Canadian going to an American school you're not eligible for US government based funding opportunities (i.e., NIH, NIMH, etc.) - essentially meaning your funding would have to be guaranteed by the university your applying to under an Research or Teaching assistantship. You also aren't eligible as a Canadian for many of the clinical training opportunities at Veterans Affairs in the US - you have to be an American citizen to work at any VA. I'm actually going to start a blog/small business that provides affordable counselling about the clinical psychology application process in Canada and US, so hopefully this will be helpful for you in the future