Go to an office supply or other store that offers the service and use a large bed scanner to scan the entire poster. Save the result as a JPEG or PNG file onto a CD or flash drive.
Insert the media into your computer. Load the image you scanned into a folder on your desktop.
Open an account with one of the several online businesses that provide print-to-canvas services, such as Cafepress, Zazzle or Canvas on Demand.
Choose the canvas size and type you want for your image and upload your image to the site. Place your order.