If the proper material for the project is available (it is) and doesn't need to be spliced, why consider anything else?
Sintra is primarily used in signage and the cold mounting of photographs. It is PH neutral and reasonably inert but is not really intended for your purpose.
Also, what about the aesthetics? Do you intend to fabric wrap? If so, be careful -
Often on larger mats (and this is LARGE) you will need to set the glue with a bit of heat, Sintra, in this case, would probably not like that so much.....it has thermoplastic qualities that make in bendable and formable with heat-