How to prevent acrylic or polycarbonate sheets from bending?
Consider tempered glass instead.
While using glass brings a real fear of breakage, thick glass actually doesn't break so easily, and it is quite strong. 2m x 3m is on the large size. Typical glass table tops that I remember seeing are more in the (at most) 1m x 2m size. I did a quick search and found a local (to me) vendor - local is important because picking it up yourself or getting a local truck delivery will be a lot cheaper than sending long distance - where this size is in the $1,000 range. From the same vendor, a table top 1/4 the size is ~ 1/8 the cost and 1/4&quot; thick instead of 3/8&quot; thick. So clearly this is a viable option, but whether it is practical or not will depend on your budget and other factors.
Glass also tends to not get scratched up as easily as most plastic, which may be a big advantage for a display medium.