Linea Sketch Basics: Canvas Size
Linea Sketch's canvas size is based on your iOS device's screen size. They are:
iPad Pro (12.9-inch): 2732 by 2048 pixels
iPad Pro (9.7-inch), iPad Air2, iPad Air, iPad mini 4, iPad mini 3 and iPad mini 2: 2048 by 1536 pixels
You can export just a portion of the canvas using the Crop and Export function.