And yeah I agree with Marthmaster's plan works very well since how I picture it the dash then the side step call still give Meta the sliding fx thus bringing him closer to Olimar yet but my only concern is that this technique works best from close to medium range and there is always the chance of olimar throwing the longer ranged white pikmin.
Medium range is about right. The thing is though, Metaknight has a pretty decent dash, so when combined with the sidestep, *if you time it right* when they throw the pikmin it'll whiff as you sidestep. that's another technique I use, as well. When my bro is busy throwing pikmin at me, i'll either do a roll towards him, then a f-tilt, or just do Metaknight's over-b, and just drill right through the pikmin and into olimar. Also, if you do that, curve it upwards to send him flying back a short distance, just so you can position your landing safely.
It's tricky, but it just requires timing and split-second thinking. If they don't have too many pikmin, sometimes it's best to take the slightly more barbaric approach, and just let them throw them on you, so you can get to them and combo Olimar. As brutal as it is, that's saved me before. They don't expect you to just charge through and attack them head-on, as that's not the normal strategy against an Olimar.
That's the biggest part of playing Metaknight vs Olimar, you have to keep Olimar constantly guessing as to what you'll do next. Just one whiff is all you need to combo him off the edge, and then off the screen.