Unlike Guile-Blanka I don’t have a lot of recent first hand experience (derrr on the other side heh) but here are some points I’ve picked up as a movie hound.
The most important thing is to have a really good sense of sim’s far crouching punch range. Back+medium kick to retreat and then sonics from just outside that range. Catch him throwing an inopportune yoga fire with a backfist or jump-in.
At that same range you can beat the far crouching strong with guile’s standing short like chun_li1 wrote above: the two-hit jab sonic -> short (kick dhalsim’s hand) combo is really beautiful.
Beat drills with standing jab, maybe back+medium kick(?). Otherwise stay in crouch when sim jumps (until it looks like he’s looking for a jump medium kick/fierce) to keep a flash kick charge.
EDIT: …or jump rh or walk underneath and crouch fierce. Read your opponent, pick something and do it without hesitation.
Jump over yoga fires (any speed?) at mid screen with jump away jab.
Sonic with charge down-back, towards, down-back + punch so as to better charge oh wait you play 3s so you already know this type of thing nevermind. Anyway canceling fire with sonic safer than jumping. The more rapidly you can throw the better.
I’ll spar with you Dhalsim-Guile whenever @ ctf if you like. When the game’s working, that is – the screen crapped out today.