Unfortunately it's impossible for you to sponsor your brother through family class. You don't meet any of the programs or requirements to qualify - and he's not classified as your dependent for Canadian immigration purposes. A medical note unfortunately won't make a difference. Sponsoring him isn't possible.
If he wishes to immigrate to Canada, he would need to qualify for PR on his own through an economic stream like Express Entry. Since it sounds like this won't be possible, you'll need to find a way to support him while he remains living in his home country.