I would say it's probably slightly easier to get into than a clinical program. However you still need a competitive application. Most people in my program had good grades and many had some applicable research and/or work-related experience. I'm not sure about transferring an MA in school psychology back to Canada, I would say that depends entirely on how the program is structured and on the requirements of provincial licensing boards. But I'd think an APA accredited PhD in school psych from the US in particular would be transferable across the boards. Keep in mind that if you are looking into US programs that school psychology there is very driven by special education law so there are differences between what a school psych looks like in the US and in Canada.