How do you select multiple photos in gallery?
To grab several at once, you can enter selection mode by long-pressing on one photo, and then tapping on other pictures or on a date. Doing the latter will automatically select all the images taken on a specific day.
How do I select multiple photos in canvas?
Click the name of the first image in the Layers Panel. This will also select the image on the Canvas. Holding down the Control button on your PC (Command key on your Mac), click the names of the other images you wish to select.