As Gary Neville has said in Russia post-match, the England strenghts are also their own weaknesses. Because yes, we could be able to find some space in their 3-5-2 but also he said how we have a better midfield than them with Rakitic and Modric when they have Alli, Lingard and Henderson.
For them, this match will be a real pleasure to watch because the both teams will attack and will play with passion.
At my eyes, yes we need to be focus on some players. Especially Trippier on the right side, his runs, his calls and his delivery are always perfect. He was unknown before his arrival in the Tottenham squad but today, he's one of the best offensive right back.
Plus the Tottenham connection is hugely present in this team and we must to contain that, not let them to play and take confidence between them. With players like Alli, Dier, Kane, Trippier, Rose, or with Walker who was at Tottenham too.
So Southgate will maybe play with the same line-up as he did in their past matchs during this world cup, with Pickford - Maguire, Stones, Walker - Young, Henderson, Alli, Lingard, Trippier - Kane, Sterling.
With Delph, Rashford and Dier as replacement for Young, Sterling and Henderson.
But yeah, as you said their set pieces are really dangerous and they're all coming from Trippier.
Now, this will be a real test for us because by the past, we had always some problems to play against this type of line-up (look at Mexico, who is playing the 3-5-2 too). And here the stamina aspect is at my eyes really important if we want to counter them because their players are fully fit and really fast with and without the ball. (Offensively and defensively).
The key will be to see our midfield join the attack and not let our 3 strikers alone up front. We'll need to play as a block and counter them as an unit. The croatian legs will be really heavy but this is our only chance to take a result from this match.
Plus Harry Kane is actually my favorite player out of our NT, and we need to be really worried about him because we can't let him 2cm front of him. This guy is clearly a lethal weapon and he is able to score with both foot, header, make the call, the right passes for his lads etc...
This will be really tough for me to see our NT playing against some players from my favorite team who is Tottenham...
But AJMO HRVATSKA !