I'm a dual citizen who did my undergrad in Canada. the PTCAS doesn't include your Canadian grades into your GPA, but most schools will calculate your GPA themselves. One school I applied to required that I have my transcripts verified by the World Education Service for my application to be evaluated. The rest didn't require this during the initial application process, and I got acceptances without it. I did however need to do it before I was able to officially enroll in my current program.
I was also curious about practicing the the US if I had gone to PT school in Canada, so I called the school that I was interested in and asked them, they told me that it generally isn't a problem for previous graduates from the program. I didn't end up following up about more details because I didn't end up going that route, but my suggestion would be to reach out directly to the school.
Hope this was helpful!