Other opinions are highly appreciated, Thanks for everyone in advance.

Thanks István Keszeg for your clear and detailed answer.

I still have some questions:

1- redirection will not be for 1 version, but for several pages (ca-en, us-en, uk-en) then would the link juice be divided on these 3 version? put in other words, will that effect our current SEO ranking for the words we are currently ranked for?

2- (point no . 2 in my first post).

Thanks in advance.

Hello all

Let me first try to explain what our company does and what it is trying to achieve.

Our company has an online store, sells products for 3 different countries, and two languages for each country.

Currently we have one site, which is open to all countries, what we are trying to achieve is make 3 different stores for these 3 different countries, so we can have a better control over the prices in each country. We are going to use Geoip to redirect the user to the local store in his country.

The suggested new structure is to add sub-folders as following:

www.example.com/ca-en
www.example.com/ca-fr
www.example.com/us-en
...

If a visitor is located outside these 3 countries, then she'll be redirected to the root directory www.example.com/en

We can't offer to expand our SEO team to optimize new pages for the local market, it's not the priority for now, the main objective now is to be able to control the prices for different market. so to eliminate the duplicate issue, we'll use canonical tags.

Now knowing our objective from the new URL structure, I have two questions:

1- which redirect should we use? 301, 302? 
If we choose 301, then which version of the site will get the link juice? (i.e, /ca-en or /us-en?)
if we choose 302, then will the link juice remain in the original links? is it healthy to use 302 for long term redirections?

2- Knowing that Google bots comes from US-IP, does that mean that the other versions of the site won't be crawled (i.e, www.example.com/ca-fr), this is especially important for us as we are using AdWords, and unindexed pages will effect our quality score badly.

I'd like to know if you have other account structure in your mind that would be better than this proposed structure.

Your help is highly highly appreciated.
Thanks in advance.