when it comes to boxing, Sean is superior against Du Plessis. they fight for 5 rounds standing and Sean will still have the stamina to carry out his strikes. he could do the same approach with Izzy to defend his title.
what could go wrong however is that Du Plessis can take him down which Du Plessis could dominate in the end. he was the first to have hyped to fight Izzy until Sean put himself in the picture. that was the time they both start trash talking then.
Du Plessis is known to be a very awkward guy to fight against. He might not seem like a great striker as he moves a bit unconventionally, but he has been very effective in his striking so far.
I remember him knocking out Roberto Soldic back in his KSW days, when he was in his early 20s. Soldic was a phenomenal striker and was undefeated, but yet, DDP managed to KO him (he lost the rematch though).
As for the ground game - I don't know. Strickland has a wrestling background and allegedly has a very good takedown defence and both seem to prefer striking, so we might not see any ground action at all.