Getting a square in 300 ppi

For large format print marketing materials like banners, posters, window graphics etc. that are meant to be viewed at more than an arm’s length away, we don’t quite need the same high res image resolution as smaller prints. You should be able to get great results as long as the images are at least 150 ppi at 100% size. Typically, the further the viewing distance is, the lower the image resolution needs to be. A billboard is typically printed at 10 ppi to 30 ppi.

Choosing the right image resolution for your print jobs - Samco Printers 

So, for an 80" poster, or especially a canvas print, 100ppi is probably just fine. Anything more than that is overkill. 80"x100ppi = 8000 pixels, which is within Fresco's 8192 pixel limit.