It depends on what game your capturing it in it will be either level 40 or 50.
You see Suicune level 50.
Suicune is at Level 40 in HeartGold and SoulSilver.
In Pokemon Soul Silver, Suicune is at level 40! ^_^
In Pokémon LeafGreen, the wild Suicune will be found at Level 50.
Suicune does not evolve.
You cannot get a Suicune level 40. Suicune cannot make eggs, and thus, he cannot be below level 40. No legendaries can be at a level lower than they are found at.
Well, if I were you, I would go into a room with Suicune in it. (but the Suicune could be low level). I did this and I got one. I hope this helps.
Lv. 40
LVL 50
You Can Find Suicune At The Maps 14,15,16 and 17 (Only In Water) I Caught My Suicune At Map 17 At Level 75, I Was Really Searching For Lugia
Suicune is a hard Pokemon to catch Suicune will move around diffrent places. You normally catch Sucune at level 40 use your map to try and find Suicune on your pokegear. It is hard but you will get there
you must then go past the bridge in cerulian city to the end there you will find suicune it will not flee and it is level:40