Is your inventory only stocked at a location in the US? If so, this is expected behaviour for the pick-up location to populate for the .com customers only. That being said, it is strange for it to display an error message on the .ca site.
If you have stock at locations in both Canada, and the US, then this definitely should not be occurring. In this situation our escalated team would need to do some troubleshooting. However, If you would like to send me your domain I can absolutely test this out for you!
In the meantime, when you send your domain, I would be happy to take a deep dive into your site to see what other support and feedback I can provide.