With a fit Davis or JWP in the side it will almost certainly be 2 from Tadic / Mane / Long. Assuming all are available for selection it will come down to the oppos defence and where we think we could get the best from Tadic and who is in the best form between Long and Mane. That leaves one up top, so far we've been lucky with both Pelle's form and no injury concerns (wood touched). Pelle will incur a suspension soon, more than likely before J-Rod is ready to return and that makes for an interesting selection for Koeman to make.
My original point about not having a back up / like for like replacement for Pelle is because I don't think our squad can afford it. It's unfortunate that both possible replacements, granted both at different levels of skill and experience, are injured.