I'm visiting Aarhus Denmark for a month and really enjoy a good curry once in a while. I've looked on Trip Advisor, but no joy.
Asian Wok Restaurant advertise Tamil / South Indian dishes that are not especially known in the west, and they appear to have the seal of approval of Aarhus's Indian community. From the way they advertise it, it looks like they do authentic south Asian food as a special rather than routine.
I'd suggest going there, not feeling too limited by the menu, and just asking them about what specific authentic dishes (particularly Tamil or South Indian) you're interested in. Independent or family run places can sometimes serve more than the popular Westernised menu suggests, e.g. they might be able to do some staples they normally only cook for staff or friends, or might be willing to serve you the more authentic version of a dish that they would normally westernise if you can convince them you know what you're talking about and won't run screaming from the spiciness or texture...
A good approach to finding things like this is to pick a dish or ingredient that is less common in inauthentic cuisine but more common in authentic cuisine, and search on that. "Curry" will always find more westernised Indian/South Asian food, for example, but a quick search on "paneer Aarhus" turned up the Indians in Aarhus facebook group. If there's a particular type of authentic Indian / South Asian dish you're interested in, search on that.
Looking at the discussion, it looks like the most reliable place to find authentic food might be cultural events. Seems like Indians in Aarhus don't find it easy to find authentic Indian food either (example).
Contacting this group directly is probably not a bad idea.
Note: this assumes you really do mean "authentic", and not "similar to Indian restaurants in Canada"...