Firstly, Troll and Yooper are the best demonyms in the nation.
Secondly, Dems need Yoopers because they don't do well with Trolls. Nominating a Troll might well be to the Dems benefit.
There are more Trolls than Yoopers in the district, at least by population. The question then becomes whether Yoopers are less likely to vote for a Troll than Trolls are to vote for a Yooper. As I understand it, the UP has the stronger identity, and might be more willing to vote for one of their own because they are their own. The Democrats nominated a Troll in 2016 - and lost.
If these are the two candidates, they are from totally different ends of the district. Bergman is from Watersmeet, near the Wisconsin border.