As I understand, the inspirations are:
Seal-tribe: Merisaamelaiset (Sea Sami, actually Norwegian)
Kuikka-tribe: Inarinsaamelaiset (more sedentary Sami from lake Inari area)
Owl-tribe: Tunturisaamelaiset (Fell Sami)
Sartolaiset: Pohjalaiset (Ostrobothnians)
Driik: Varsinaissuomalaiset (Finns proper)
Koivulaiset: Hämäläiset (Tavastians)
Kiesseläiset: Savolaiset (Savonians)
Reemiläiset: Karjalaiset (Karelians)
Kaumolaiset: Kainuulaiset (not sure there is established English term? Kajanalanders?)
The Islander's are pretty vague, though since they aren't said as speaking a different language the implication is that they are akin to Driik rather than being Norse. Personally I often give them bättre folk (i.e. Norse) names, though. Like Gandalfr, good islander name if there ever was one.
In general the in-game takes here are more in place in 19th century national romanticm than historical iron-age Finland. Like colonization of Savo by Tavastian migrants (there was actually some results of large scale genetic study published recently confirming that they were indeed Tavastians, not Karelians) was something that was still ongoing in early modern period, to say nothing about Kainuu which was definetly still Sami territory. And then we have the puukkojunkkari Sartolaiset (knife junker, 19th century Ostrobothnian rogues, folk anti-heros). So you could look up on Finnish national romanticism, especially the book The Seven Brothers by Aleksis Kivi if you can find it. And of course Kalevala, a far less accessible collection of poetic literature edited from basis of mainly Karelian folk poetry.
Personally I like Kuikka-tribe, Kiesseläiset and Islanders. Good mix of skills and competent but not sky-high combat skills.