I can not speak to the service experience greatly since I have only been to the service department twice in 11 months now. Once for the tranny programming upgrade and once for a tire rotation but I have been pleased with the overall experience so far at Valley Pontiac/Buick/GMC in Apple Valley.
There is a Buick dealer north of Minneapolis. The owner is Steve Whitaker and is an aquaintance of mine. He is a third generation Buick dealer and recently relocated north of town a short ways. I think it is north. Knowing him, I am certain he intends to run a top notch service department. Why not call him and tell him Galen Shields from Kansas has referred you. He'll remember me as the one who sold him that beautiful custom 1966 Riviera (black) last year. He really is a very nice fellow and easy to talk to. Let him walk you to the service department. That should start you off on good footing.
Buick puts out a magazine for new owners periodicaly and an Enclave owner was featured from the Minn. area who described a scenic trip they took. They mentioned having purchased it in that area, so I emailed Steve, and sure enough his store had sold that car. Interesting as they mentioned having had a good experience.
I live in Aitkin and bought my Enclave and have had it serviced at Stillwater Motor. Their service techs are top notch - had an air contioner leak that required the removal of the dashboard. They have about 10 Enclaves in stock - see Todd Peterson. I now have 16,500 miles on the odometer.
So far I have had a great experience at Lupint Buick of Golden Valley http://www.lupientbpg.com/ They have many Es to choose from although I choose to factory order to get exactly what I wanted. I have no experience with the service department since I will not take delivery of my E until the first week of March.