Hello Derek,
Thanks for your interest in working with an API and QuickBooks Payments Canada. I'm glad to hear that you've already been doing your research to dive into this process and learn what steps you need to take. I'll point you in the right direction.
I have a feeling you've already come across it, but if not, check out the Intuit Developer website to learn more about this process. When what you're seeing there leaves you with more questions, you can post in the Developer forum, which is much like the QuickBooks Online Community forum right here! While I'm available to answer QuickBooks technical support questions in relation to using the program, those answering in the Developer forum are able to let you know about the development side of things. The Developer forum is here: Intuit Developer Support
Finally, there's also an email you can use to reach Intuit Developer Relations: [email address removed]. Using these resources should get you to the people who can answer with more detail the options for API options and QuickBooks Payments Canada.
Wishing you the best with this endeavour!