Does it matter if I use White Lilly all-purpose flour or King Arthur unbleached for a bundt cake?

For a bundt/pound cake, I probably doesn't matter. but White Lily is a softer wheat flour with less gluten. It produces more tender cakes and better pastry than the harder wheat.

Some people prefer bleached flour for cakes because supposedly it helps them rise a bit more, but I only use unbleached flour (usually KAF). I think unbleached works perfectly, even with light, fluffy cakes, and there's the added bonus of avoiding the chemicals that are used for bleaching.