Mezue ahịrịokwu na-esonụ: N'ihi mkpọchi NHL 2012<unk>13, ndị Leafs tọhapụrụ Gunnarsson iji soro ndị otu obodo ya Örebro HK kpọọ oge egwuregwu. Mgbe mkpọchi ahụ kwụsịrị, Gunnarsson laghachiri na North America wee gaa n'ihu n'oge ahụ na Toronto Maple Leafs. Agbanyeghị, oge ya n'usoro ahụ adịteghị aka ka ọ na-agwọ ọgwụgwọ iji weghachite mmerụ ahụ ikpere mgbe ọ na-egwu egwuregwu asaa. Gunnarsson ka enyere ikike igwu egwu maka Leafs tupu oge 2013-14 wee mee usoro mmeghe ha. Oge ahụ ga-abụ nke ikpeazụ ya na Maple Leafs, dịka na 28 June 2014, Gunnarsson na nke anọ nke draft draft na
2014 NHL Entry Draft gbanwere na St. Louis Blues na mgbanwe maka onye na-agbachitere Roman Polák. A wara ya ahụ n'úkwù n'oge oge ezumike ma a kwadoro ya n'ụzọ ahụike ka ọ kpọọ na 14 Ọktoba 2014.