I will cheer for whoever wins their qualifying heat.
No matter who it is, I will cheer for the person who wins their heat.
ーI will cheer for whoever wins their qualifying heat.
「誰が予選に勝ってもその人を応援します」
to cheer for ... で「…を応援する」
qualifying heat で「予選試合」
ーNo matter who it is, I will cheer for the person who wins their heat.
「それが誰であっても、予選に勝った人を応援します」
no matter who it is で「それが誰であっても」
heat で「予選」
ご参考まで!