The Pacquiao of a couple of years ago smokes Garcia. Despite his skill at countering and underrated defence Garcia is a bit too flat footed and a bit too slow. Pac gets in and lands shots before Garcia can counter them and if Garcia starts to come forward Pac likely walks him onto something.
These days, it's harder to tell. There's only been one bout since Margarito where Pac has really looked good... and in that bout he ended up knocked out in six rounds. He was underwhelming against Mosely and Bradley (whoever you thought won) and in many of the rounds only really came to life in the last 30 seconds. The concern if he boxes that way against Garcia is that it gives Garcia 150 seconds at the start of each round to start working out his range and timing... and it also means that if Pac doesn't convincingly win those last 30 seconds he's likely to lose the round.
In his most recent bout against Marquez Pac looked a lot better than he has previously; the intensity and fire that was lacking from the earlier bouts had returned. The cost of this though was that he became wild... arguably wilder than he has been since moving up from 122lbs... and that meant he walked onto shots. And while Marquez might want to be the one boxer you don't want to walk onto shots from, Garcia can't be far behind. The question then becomes can Pac hurt or stop Garcia before Garcia detonates something on his chin... and that's a harder question to answer.
I don't think the question will be answered in his next bout. Rios is tailor made for Pac, a crude pressure fighter who simply walks forward (not particularly quickly) and tries to draw everyone into a brawl. He's a smaller version of Margarito and, truth be told, Rios hasn't actually looked particularly good in a bout (however exciting the Alvarado bouts were) since Urbano Antillon. Pac... even if not at his best... should be able to shred Rios coming in and then get out for there before Rios can get any of his shots off. The style matchup is just so much in Pac's favour that if he even struggles it's a really bad sign.
I'd still pick Pac over Garcia. He's still quick, he still hits fairly hard, he can still rip opponents apart and I think Garcia is just that little bit too slow to handle him. But it's not the one-sided beating it would have been three or four years ago.