Guile is a good matchup for Vega. You have a lot of options to get through his fireball game, and once that’s dealt with, there isn’t much else he can do.
Usually the match goes like this: Guile tries to establish his sonic booms, you jump them and slowly push him into the corner and eat him alive with long range pokes.
When Guile throws a boom, you can A) Slide at him which often trades, B) C.MP early to hit him out of it, or C) jump in. He recovers fast enough to block your jump in, but not fast enough to get out his C.HP antiair, so just do a blockstring and push him back.
Once you have him in the corner, stand outside his C.MK range and fish for opportunities. C.MP, Slide, Jab Roll are all good. Sometimes you can predict a sonic boom and get a J.MP, C.MP combo. Mix in a lot of neutral jumps at this range, where his Flash Kick will miss and you can punish him. Once in a while sneak in a throw after a Jab Roll or poke. In general, he’ll take more damage from your pokes than you will from blocking sonic booms.
The only thing time you should be worried is with the top level Guile players, who are extremely basic and precise. They don’t throw bad sonic booms which are unsafe, and will reliably Flash Kick all your attacks. Top Guiles can also play aggressively well, and throw Jab sonic booms into throw mixups. You have to match by tightening down your game as well. Throw in fast normals like S.LK to bait out Flash Kicks. Don’t jump in anticipation of anything since Guile will always have antiair ready. Establish purposely weak strings like Jab Roll, C.LP, Jab Roll. Let him interrupt this with a Flash Kick once or twice, then stop the 2nd Jab Roll and he’ll often still react to it.
- Flash Kick has a hitbox which reaches a little behind him, so you can’t Wall Dive off Guile’s wall when he’s in the corner. You need him to be a step or two forward before trying it.