In the last two fights Maidana was able to cut him off easily but he was too slow to connect with any significant power shots. If he gets cut off by Pacquiao he's gonna have issues with speed. The Zab Judah fight also exposed some of Mayweather's weaknesses.
The simple truth is that Floyd is in his late 30s. Maidana was able to land more punches against him in that first fight than anybody previously (and at a good percentage), and he hit him with some bombs. If Maidana was able to wear punchers gloves in that first fight it may have made a real difference. (Floyd had a hissey fit on the day of the fight.) Maidana landed some bombs in the second fight as well but Floyd did much better. Floyd's path to a legit victory is to stay on his toes and go backwards, popping out shots at range with selective counterpunching. If Floyd touches the ropes or goes into the shell he will get ripped from the beltline to forehead... Heck, even if Floyd can stay on his toes and go backward Manny still might catch him. Manny is still fast, highly dynamic, has great feet, and still has power despite the lack of recent KOs. A boring fight is a Floyd win.
Anybody buying this fight should also keep this in mind: It is on Cinco de Mayo in Las Vegas. That's the weekend Floyd likes to fight, in the city he likes to fight in. The economics of it say that a 'controversial' Floyd 'win' is actually a highly desirable outcome. For Manny to win he will have to beat Floyd from pillar to post for 9 rounds, or knock him down a bunch of times, or KO him. Anything semi-close goes to Floyd.
Personally I'll be cheering for Manny. While both fighters are on the decline, people overemphasize Manny's KO loss to JMM where he was breaking JMM down up until he ate that counter, and his theft loss to Bradely. Frankly, I think there's a good recipe to roll Floyd up in his shell now if he's dumb enough to go that way, and he's slower on his feet if he doesn't. He also doesn't have a JMM type 'one shot counter' like that in him. Despite the Vegas odds (that have long over-favoured 'modern Floyd') I think Manny has the goods to get this done. With that being said, a lot rides on who shows up on fight day in each case, and I wouldn't bet on a fight where one guy in all likelihood has to clearly win 9ish rounds to actually win (or get a bunch of knockdowns, or a KO).
That's my $.02 anyway.