In a medium saucepan, combine the soymilk, sugar, and maple syrup over medium heat. Cook for 5 minutes, whisking often.
In a small bowl, whisk together the cornstarch and water, then add to the saucepan. Cook caramel for an additional 5 minutes. The mixture will bubble, foam, and thicken somewhat.
Remove from heat and whisk in the soy margarine, vanilla extract, and kosher salt.
Transfer to a heat-proof container and leave the lid ajar until the caramel comes to room temperature. The caramel will continue to thicken as it cools.
Notes
TO STORE: Refrigerate leftover vegan caramel in a sealed container for up to two weeks. Stir before using.
TO REHEAT: Warm gently on the stovetop or in the microwave until warm.