If that's too easy for you, you could also experiment with balloon mods to bring one up to the roof or use a Próspero Sky Crane.
In that case, leave the area and when you're back, the vehicles should have respawned. Some require many tries, so many in fact that the player might use up all the nearby vehicles trying to complete the stunt. Otherwise, certain speed stunts also unlock vehicles. Some of the stunts unlock a vehicle by driving through them. These include the Fishing Boat, Armadillo Crane Truck, and a few others. Some of them only have one stunt to unlock them in supply drop. Examples include the Emsavion Utility Heli, Mugello Pescespada SX, Caravana Camper, Prisa Tía Moped, and a few others.
In these cases, try using the balloons and boosters on the grappler to make the vehicle fly/float through the ring (you might have to unlock some of the grappler mods to customize the balloons and boosters so that they work correctly during the stunt). For ground vehicles, there is usually a ramp, but the specified vehicle might not be able to fly off the ramp and through the ring - more often than not, they drop short and hit the ground before reaching the ring. Often, the difficult stunts are the ones where they require a ground or sea vehicle to pass through a ring several meters in the air. These stunts are anywhere between moderately easy to extremely challenging. Sometimes there isn't one nearby, necessitating a supply drop run or having to bring one from another area. Normally the vehicle is within 100 meters. In these stunts the required vehicle is most of the time parked nearby, even if the stunt is located in complete wilderness. These stunts range from very simple ones where the vehicle has to be driven through a loop at any speed to having to jump through a loop at an odd location. In JC4 most vehicles are unlocked at the supply drop by completing some "stunt" with them. These stunts are tied to completing the nearest settlement. If not, open the map and press on the icon of the stunt to track it. When near a stunt, the player will be prompted to track it by pressing some button. These can be seen with the AR scan, but have to be "tracked". Without mods to facilitate the process (such as additional wingsuit boost for wingsuit stunts, faster vehicles for speed stunts and vehicle spawners for vehicle stunts), it would take dozens of hours to complete all stunts. There are 124 wingsuit stunts, 185 speed stunts, and 127 vehicle stunts for a total of 436 stunts across Solís. And in some cases, some are unavailable until a vehicle is unlocked in supply drop. While most of them are easy enough, some of them require careful timing and precise setup.
These points can be used to upgrade the grappler's booster mods. Doing stunts not only "completes" a settlement but gains Garland points as well. Stunts are assigned by Garland, who needs Rico to perform daredevil stunts for her movies. Previously liberations filled the purpose of "completing" settlements. Region strikes will occupy the region, but doing all the stunts will mark the settlement as "complete".
As of JC4 they are actually needed for 100% settlement completion. Stunts (see improvised stunts) have always been a major part of the Just Cause game series.