Some quick background about Sun Country:
Sun Country Airlines is a United States-based low-cost airline headquartered in Eagan, Minnesota and based at nearby Minneapolis–Saint Paul International Airport. The airline operates 70 routes, mostly between destinations in the United States, Mexico, Central America and the Caribbean.
Now that is out the way here is the livery!
Photo Credit go to Nick Benson: https://jettip.net/blog/sun-countrys-current-liveries
The livery is on 2 aircraft so far. The livery was voted on by employees which was talked about by @Balloonchaser in this post. It seems the IF community voted similarly to the employees. The blue on the aircraft is taken from a depth chart of Lake Minnetonka. This is probably to relate to the now discontinued practice of naming their aircraft after lakes.