Quote from Rakath »To further confuse this, as I had a question regarding Adventure answered:
Cascade works off the CMC of the creature to determine if you cast either side, but Electrodominance works off of whichever half you're trying to cast.
So it seems to be a matter of how selection is being done. If you're choosing a spell to match the conditions broadly (say: Haakon, Kess) you have to match exactly what they want (Knights, Instant/Sorcery). But if you're presented with a card and it checks for a detail (in Cascade's case: CMC) then once that check is done the entire card passes, either side works.
Quote from cyberium_neo »Another interesting info I read about Sigarda's Aid: https://blogs.magicjudges.org/rulestips/2016/08/bestow-and-sigardas-aid/
"Rule 601.3b tells us that if an effect allows you to cast a spell with certain characteristics as though it had Flash (like Sigarda’s Aid for Auras), you’re allowed to factor in choices you make later on in the spellcasting process, such as choosing to use Bestow."
So how does this interact with rules like Haakon/Kess and Adventure spells? I presume the process of casting a Bestow creature as aura is similar to Adventure, both are creature cards in their basic state, so if Sigarda's Aid allows you to cast bestow in instant speed, wouldn't Haakon allow you to cast the Adventure part of a knight?