Sundre graduated from Mahnomen High School in Mahnomen, Minnesota and Mayville Teacher's College—now known as Mayville State University—in Mayville, North Dakota. He earned a master's degree from the University of North Dakota in 1960.[2] At Ellendale, Sundre also was the head wrestling and track coach. He returned to Mayville State in 1963 as head coach in wrestling, golf, and tennis.[3] He was also an assistant football coach at Mayville State for three seasons, from 1963 to 1965.[4]