What happens if I’m running the Proton VPN client on Mac Os connected to a U.S VPN server and than startup the Proton VPN browser extension connecting to a VPN Server in Canada. What really happens? Does the VPN client overview the browser extension? do they act separately?
I’m trying to understand the behavior.
-D
running vpns inside vpns can be tricky and when it works you will probably feel an impact on your internet speed. If it works I’d expect traffic through the browser appearing canadian and though other apps american.
this is easy to test: start computer, open browser search “what’s my ip” on your engine of choice, start the browser extension and do the same search, with the browser extension on, open your terminal type “curl v4.ident.me” and check it matches the result of your first search.
A good way to stack VPNs is using a VM, one VPN in the host and another in the VM. A VPN capable router is also great.
Does the vpn client encrypt the browser tunnel.
Actually you are right. I tested it looks like they both act separately, which is great!
OP also runs the risk of ripping a hole in spacetime which would doom us all. If you really want to tunnel one VPN through another, use two different providers. The universe will thank you.
see u/BuckNastysMamma’s comment.
in your setup not only you’re encrypting everything twice your packets should be getting a few extra headers: it’s like you wrote a letter, put it in an envelope with the recipient’s address, encoded both into a secret code only your canadian friend can decode, then put into into another envelope with your canadian friend’s address and encoded everything into a code for your US friend can read, put those in an normal envelop addressed to your us friend and mailed it. The postie gets the letter to the US. Your US friend decrypts everything and now has a normal envelope with a canadian address containing an envelope with a letter in canadian code, which he sends to canada. Your canadian friend decodes everything into plain english and sends it its final destination. 
in short, not the most efficient process in the world. you may feel the lag in our browsing but even if you don’t this also puts some extra burden on the network. ideally you’d connect to the US when you want the US, and canada when you want canada. or, if you always want both have separate machines connected to each. or have 2 proxies connected to separate VPNs on the same machine… I’ve been thinking of setting up something along these lines (2 proxies) myself but haven’t got round to it yet.
not separately, one inside the other so your speed will slow down. 
systemwide vpn client + tor browser + browser vpn extension = connection annihilation by peer
what’s the difference between 1 or 2 providers?
It’s just a joke. Sorry to lead you astray.
I thought the first part was a joke but the second was serious
It’s hard to come up with a scenario where two simultaneous commercial VPNs makes sense from the same device. Tunneling one within another, the outer one becomes useless.
you’re extremely paranoid, subscribed to each of them with paycards you bough in cash using sunglasses, a baseball cap and a wig?