Not sure of any recent changes through GOG about using these cards to put funds on my account. Anyone have news about this would help me to get Witcher 3 stuff before sale expires :)

Take a look at the packaging and the small print on the back.
In the US you usually can't, but, on the ones I've seen at least, it says quite clearly somewhere on it that the card cannot be used for international purchases.
Not sure about Canada, but I would imagine it will say you can't somewhere on it if you can't.

If you already have the card you can just try it, and it will just be declined if it won't work. (Dunno about per purchase charges that the card may have on it, read the fine print I suppose.)
There may also be some kind of contact number on it that you can call and ask about international purchases.

It's on their website:

https://www.vanillaprepaid.com/

FAQ here:

https://www.vanillaprepaid.com/VanillaPrepaid/faq.html Their VISA support line: 1-844-864-6951

On and I would suggest asking about "international online purchases", not"international purchases"

Good luck.

Having said that, yes, credits cards that are restricted to certain countries like US and/ or Canada will be rejected since GoG is Europe based. My payroll Visa is rejected, even with Paypal.