Hello... Me again... Is there a site that shows what level the bosses..

I can tell you the recruitment rate, but not their HP or level. Sorry!
ZAPDOS-Likely
ARTICUNO-Likely
MOLTRES-Likely
RAIKU-Unlikely
ENTEI-Unlikely
SUICUNE-Unlikely
LUGIA-Very Likely
HO-OH-Very Likely
REGIROCK-Unlikely
REGISTEEL-Unlikely
REGICE-Unlikely
LATIOS-Very Likely
LATIAS-Very Likely
KYOGRE-Likely
GROUDON-Very Unlikely
RAYQUAZA-Very Unlikely
That's all I know...
(P.S.Most of theese you can't catch on your first try a.k.a. You can only catch them after beating RAYQUAZA for the first time.)

I know Zapadoes has 300 when you first battle it and is level 25, so from there you can kind of get a picture that they will grow in levels, and will be much higher.

Your leader must be of a higher level than the Pokemon you are trying to recruit, so it's annoying that this info is hard to find. I'm going to record the level of every legendary I recruit from now on and maybe we can get a complete list. I can tell you 3 levels for sure:

Zapados-Level 42 (likely)
Moltres-Level 43 (likely)
Articuno-Level 45 (likely)

All 3 were pretty easy to recruit, by the way, 2 or 3 tries at most in my case.

I'll try to post more as I get them organized, probably in walkthroughs...not much time lately to do stuff like that.

I think I may have given the wrong levels earlier in my answer, so please disregard and these are the correct levels the 3 birds will be at when you try to recruit them:
Zapados-Level 45
Moltres-Level 52
Articuno-Level 53

Oh, and these are from some of pimpblue's answers: (TY! Pimpblue!)
Deoxys-Level 35
Ho-Oh-Level 50

Sorry about the mistake!