it's an interesting call to put scott at 6 and Cane on the bench. I can see some reasoning for it.
1, importantly and maybe the main reason Cane was subbed for barrett early against ireland is that with Savea at 6 we lose strength at the lineout. IMO Savea just shouldn't be jumping that should have been left to Read, Sam and Guzzler with some change up options. So far this WC the AB's have been using Savea and we have lost at least 3 lineouts that have been thrown to him, Ireland got one in the first half. Starting Scott at 6 fixes that. It's something England would have seen and targeted.
2, the loss of Todd changes the dynamics of the bench, the alternative was having Scott and Patrick on the bench - two locks, or the less experienced Frizell. But Tuipulotu has been in great form and his Physical impact will be an asset off the bench later.
3, Sam Cane has never played England in his 66 odd tests, for various reasons and injury timing he's missed out. I don't know how much that fact plays into the selection. I doubt that would phase him he will be looking forward to it.
4, Cane seems to be less of an 80min player than Savea in test rugby. It's not that Cane is unfit its more to do with cane being the guy who puts his body on the line more than most stopping the big opposition ball carriers, slowing ball and cleaning rucks. I think late in games when we are ahead it makes sense just to bring him off and preserve his body a bit from the punishment he takes.
What we give up?
Sam Cane is not the flashiest 7 in the world, he's solid all round with one distinction. He's probably the best defender in the NZ game arguably the world. Against Ireland Savea topped the All Blacks tackle count with 14 in 80minutes. Sam Cane made 12 in his 40 minutes heading for his usual 20 odd he often gets in a full 80. It's not just the number though, he brings guys down before they get to the advantage line. He's great laterally as well and his tackles sting. And he sets the standards for defense early in the game. Savea is a great defender but he's not Sam Cane, against SA the biggest break the boks made against us was after Half time and Cane was in the HIA mixup, Savea moved to 7 and Vermeulen ran straight past Savea in the 7 channel. I don't think people appreciate just how good Cane is in that area. As most keen eyed All Black arm chair analysts will know - in that first few minutes if the All Blacks forwards assert some dominance in the tackle and start trapping ball carriers behind the gain line you know its time to sit back and enjoy what is almost certainly a win.
Barrett is a prodigious talent though, he has spent plenty of time at 6. The Crusaders have Barrett, Whitelock and Romano. With 3 great locks there Scott splits his time between lock and 6. He has a huge gas tank and workrate.
On another note, still sad not to see Bender I think he would be a good bench option for this game.