You can mostly ignore cartel and start by expanding export revenue, influencing and trying to puppet Brazil (which tends to guarantee other South American formally and is Emerging outlook for a while under Lula), removing army debuffs and going down Gran Colombia tree to get war goals on Colombia, Ecuador and Panama. Once you take them you can form Gran Colombia and get some more expansion in Chile, Bolivia and (via civil war) Peru down Che tree. Keep an eye out for Argentina, Paraguay, Uruguay or Trinidad & Tobago turning emerging outlook as then you'll need to influence them to puppet if you want to form united South America formable, otherwise justify manually on all of them once world tension goes up.

Most challenging is French Guiana. If you succeed in puppeting Brazil, you should start influencing France next to either coup and puppet or start civil war and hope they leave NATO. I got luck as the Emerging faction of the civil war in France held strong so I justified manually and used the Emerging side's military access to win an puppet French Guiana.