Should I Use Primary Domains For Multiple Target Countries (Using Same Language)?

[Shawn512]

Background:

My primary market is UK, I also want to expand to US / Canada / Australia (English-Language countries)
Question:

In such case, whats the best domains solution for SEO & User experience? ( I use shopify payments to solve currency issue)

1, I use only Primary domain, for all the English-Language countries.

2, I use subfolders , like xxxx.com/us, xxxx.com/ca for different countries, even they use same launguage.

Thanks