We would like to have all of it on www.mydomain.com/subfolder (where subfolder would be : blog, pro, resources).
Obvisouly we can't move the B2C website on Hubspot.
So i understant i'm looking at a reverse proxy.
On their Doc, Hubspot said they don't support it.
I'm looking to testimonials of people who did it ?
Here is Hubspot answer : I understand that your looking to set up a proxy to regroup your websites. Or even looking for a possible workaround to be able to do this. After partnering with our team it seems as though the universal answer is just that it is not a sustainable idea when using HubSpot. Im sure you know this already but with the single IP address and multiple requests our firewall assumes its a DDoS, assumes its a "bad actor" and will shut it down. As "Dadams" mentions in the forum you sent, this may not happen immediately but it could happen over time. You can definitely post your question in the forum and try and collaborate with other users, but HubSpot truly suggests it is not a sustainable idea.
I don't have much to add here outside of the response you've gotten from HubSpot already, but I figured I'd jump in just to reiterate that a reverse proxy isn't supported, and can compromise the performance/security of the HubSpot CMS. You'll likely run into blocking issues with the HubSpot firewall/DDoS protections if you decide to go down this route.