What do you base this information on really? Neither Denmark or Sweden are part of the eurozone. Their currencies are Danish krone (DKK) and Swedish krona (SEK). My Sweden experience is that practically only exchange offices (and banks maybe) will touch cash euros.
Edit: Sure, large players of the underground market might accept euros, especially in inter-European trade. But good luck "banning" them from using such and such notes among themselves.
Edit: Sure, large players of the underground market might accept euros, especially in inter-European trade. But good luck "banning" them from using such and such notes among themselves.