One of Samsung Canada's Managers (@Steve01) has said something to the effect that Samsung Canada isn't able to provide support for the Betas, presumably he meant that should people have problems, Samsung Canada's suppose isn't up to the task.
You can't join the US Beta unless you have an account with a US Carrier (not sure if they also check the IMEI to make sure it's a US device?)
I guess that Samsung is looking for a reasonable cross section & larger markets like the US for Snapdragon variants & the UK, Germany etc for the Exynos version. There ARE countries of similar size to Canada, who are part of the Beta programme, but if you've read comments here regarding Samsung's Chat support, or the often misinformed posts by a number of Samsung Members Moderators, I think that there's a valid reason for Canada not being part of the Beta.
If you know what you're doing, you can always Flash the CORRECT version of the US Beta Firmware when it's available for your device.