Hi James
I do not have an employee engagement survey template to share I'm afraid, but would like to give some advice at least.
First and foremost: If you want more open and honest answers, more action following the survey, and someone who can turn results into value, find a good provider instead of sending and conducting the surveys yourself. Of course, I can't recommend anyone here on these forums :)
Also, focus a lot on verbatim comments and not just some average results over satisfaction rated 1-5. Put much emphasis on the free text fields and actually consider everybody's comments, don't ignore anything. A simple sentence adds so much more to a result that reads "1 - Very dissatisfied".
Another key point is to assure anonymousity, but I assume you are well aware of that already.
Finally, share the results with everybody and don't keep them for yourself and the senior management!