From a site called "fitday.com":
Full-fat coconut cream can be used as a substitute for crème fraîche, but it will add a different flavor to the meal. Alternatively, soy sour creams can also be used. A blend of vegan cream cheese with a small amount of soy milk, or another sort of vegan milk, and lemon juice will also make a crème fraîche substitute that is similar in taste to the original.
and from "tastebook.com":
Vegan Heavy Cream (Crème Fraiche substitute):
For those who love the idea of a big dollop of cream on top of your favorite soup. Try this guilt free delight. This is perfect for savory dishes requiring heavy Cream or Crème Fraiche.
I use this for almost any dish asking for Cream, Sour Cream or Crème Fraiche
Add a sweetener of your choice for sweet desserts
1 cup Tofutti Cream Cheese (or other Vegan Cream Cheese)
2 1/2 tbs almond, rice or soymilk
1 tsp of lemon or lime juice