For the record, I'm very big on Finnish acts overall because the language is very pleasing to the ear, despite me not speaking a word of it. And even if they are singing in English their singing accent sounds quite.. cute. Depending on the singer of course.
I find that certain singers, in trying to prevent an accent, have a very articulated way of pronouncing words while singing.
Tarja Turunen, Klaus Meine, Agnetha & Anni from ABBA. All of them have strong accents while speaking and Klaus' comes through the most while singing, but not strongly.