Vacation in northern Norway/Sweden/Finland in March - Suggestions??

Thinking about celebrating our 30th wedding anniversary visiting Norway, Sweden, and Finland next March. My wife is bonkers for Northern Lights and we don’t get much of that here in Michigan, USA. If we go, I’m going to try and surprise her, but when I tell her what to pack she might have her suspicions.

Open to suggestions and what to visit, but will be a fairly low key vacation - we love the outdoors and not real fond of cities. If we make the trip, seems like we should at least try to hit a few different countries. Open to travelling by train around the region or renting a car. Would like to spend most of the two weeks in the northern parts for viewing Northern Lights and do some snowshoeing, snowmobile sight seeing, dog sledding, etc. I should stop by Mindark, but don’t think they allow visitors.

What suggestions do you all have for locations to visit, stay, etc? What’s on the “must see/do” list?