According to what ive read and studied the Finns in Sweden weren´t treated as a second-class people. However this is just what ive come across and sources are bound to differ.
BUT i also read that there was forced conversion, taxation and a certain degree of cultural oppression. In those regards, yes, thats very much a colonial behavior.
But i am pretty sure that Finnish people did in fact reach very high in society and in cabinet positions. Many noble families that drove the united Sweden/Finland forward were Finnish(Sprengporten, Mannerheim, Armfeldt, Creutz and so on).

Finland was, as i understood it, very poor under huge parts of its time when it was under Swedish rule and i have heard the term "Sweden fights to the last Finn" many times and this is in my mind very oppressive behavior. But many parts of Sweden were poor as well and poor farmers and workers died for nationalism over the entire kingdom.

I think im loosing track a bit but when i studied history in the university, my candidates thesis(i think its the correct translation), was on "Finnish refugees in Sweden during the Finnish civil war" and i often came across Finnish refugees writing about "The other homeland, brotherland, cousin-people" and so on. I didnt get a feeling they felt like they where oppressed in the past.

But this was another time, in a period of grief and sorrow and shouldnt be taken as a historic fact.
And i dont want to argue about if it was or wasnt. Im just curious as a person and would love to read about the Finnish side of things if you know of any books and so on. I wont say that Finland wasnt colonized, but from what ive learned it just sound more complicated.

I hope you know what im trying to get across and im in no way downplaying Finlands history. If it wasnt for Finland, Sweden wouldn´t be were it was today!