Which junglers can I take that can resist Janna's denial mechanic well?

Olaf doest get kited, Olaf kills those who try...

Janna stops everyone, maybe try some type of ranged jungler. Otherwise, don't gank a lane with a Janna unless you have your ult. maybe, since sej has some slow resistance and evelynn can burst down the adc before janna can react.

Vi also is a good pick with her ult and high dmg. Other than that if you have flash and a knockup that's also a choice, only do it if it's for the better of your team of course. The knockup will stop any further healing making her fairly useless in a team fight.

If you're just looking to not get popped up by her Q mid-dash or get blown away by her ultimate, then ulting Olaf's about the best way to approach that.

Maokai but not really

ranged junglers. don't pick any melee jungler against janna. well in low elo it usually doesn't matter but its still annoying. idk kindred or graves possibly.

you usually wanna kill healers like janna soraka etc before u kill the rest because they will just make it harder/not possible

Yeah as a janna main, your best bets are Olaf with ult, Vi with ult, and perhaps malphite/sion with their ults.

Olaf I can't do anything about beyond shield the carry and hope for the best. Vi I can peel post ult but often the ult damage+lockdown in conjunction with enemy bot lane is enough for the kill, so I might be forced to ult early for the heal, leaving only q to peel off from there (plus many jannas might try to q the ult anyway in the heat of the moment). Malphite/sion aren't that bad since their ult burst usually isn't enough on its own, but I can't really stop it.

Or do whatever with a morg black shield, that'll usually usually frustrate me for a bit until it wears off or the shield is popped.

Edit: Honourable mentions to noct and panth with their respective ults. Noct can get in and spellshield the peel (and even get bonus AS from it), and panth can show up in a spot where peeling with ult isn't practical, and the nado isn't necessarily enough.

Can all go straight past Janna and just start hitting things.

Master Yi does fairly well because he can close the gap with his ult and then Q back in the moment he gets ulted. If you ever see Cowsep play against Janna; that's pretty much how he handles the situation every single time.