You can load url's for sprites, tilemaps and tiledbackgrounds, for example.
The canvas plugin is very similar to tilemaps, but works with any uploaded image without the need of these additional steps.
You don't need to worry about arrays for this simple task, because a simple math is enough.
The size of each image will be previous know? Do you know how much images you want place on the canvas?
Imagine the canvas divided by slots and give each slot an ID, you'll know each position by its ID and you will be able to place them on the right position. Store the id and position with instance variables.
If you hate math, you can use an invisible tilemap on the background with previous size determined (but you'll be able to change it at runtime if necessary), so, use the tiletopositionX(tileID) and tiletopositionY(tileID) to place you image on the desired tile.