Design Disagreement

I'm a mid-level engineer working on the design for a ~2 month long project. There are three other stakeholders involved in this (two L5's and an L6 who have been at the team for a while) and we've been discussing this project for the past ~3 weeks. My manager was on vacation and just came back.

Based on discussions over the past few weeks, I have a proposed solution. My manager (he has joined ~4 months ago) disagrees and has numerous concerns. So does another L6 who joined the team who he (presumably) asked to look at the design. They have a suggested approach that differs from mine.

The two other L5's and L6 on the team for a while generally agree with my solution and are unsupportive of the solution posed by my manager.

We had another discussion and left off with the conclusion that I am to speak with some engineers on core infra more familiar with the feasibility of my manager's solution. Ultimately, it's been decided that I will make the call on this by end of next week.

It's a significant, foundational project with large ambiguity and complexity, so the stakes are somewhat high.

What should I do to resolve this? I've added both L6's to the call with the infra engineers early next week. My assumption is that the infra team will say that alternative solution is not feasible.