what does he do usually when you run in with an attack? does he sheild grab you or does he intercept you?
if he is intercepting you and you read it, you can simply dash backwards (assuming you're fox trotting) and then grab him during his move's lag.
many newer players don't recognize that even though lcanceling makes things seem a lot faster, there is still a 10-15 frame window where the opponent can't do anything. this is one of cf's primary methods of combo starting: bait and punish. bait falco's shine, dair out of shield and combo. bait marth's fair, dash in and grab. its the same tactic.
and if he shields when you approach just grab him. if he rolls read his pattern (people who have gotten away with it for a long time will habitually roll behind you, which happens to be the easiest to punish)
if you are uncertain what he will do, try spacing your nair. when doing this, its better to end up too short than go too far forward. the nair has lots of range in front and covers you for your whole short hop. if you DI backwards and wiff, it is unlikely that they will manage to cover the distance to punish you for wiffing. if you go against his shield, you want just the tips of your feet to hit it, and land so he cant grab. if that fails buffer a dodge or jab.
once you get the first hit, you should be able to combo from there.