I have a website and I blocked 3 countries visitors using htaccess. I need to use Cloudflare at this moment. But I don't want those 3 countries to visit my website anymore. If I use Cloudflare, will it unblock those 3 countries?
I think it unblocks previously set countries, I am not sure. If it does, you can again block those countries using Cloudflare. Check this out.
Assuming that your .htaccess configuration probably uses the source IP address to detect from which country the connection comes, with Cloudflare in front of your website, that IP will belong to one of our datacentre, and therefore be marked as coming from the US. So, yes, this will affect the current behaviour.