Today I want to share with you the "Ars Fantasio" way of doing just that;).
There are numerous sources on the web that have solutions for corners that don´t have to be cut, but what I hate about that solution is that the back of the frame will become very thick very fast.
Even with a thin canvas of 280g it becomes annoyingly thick and I will not want to have a art piece on a wall where the middle part is standing 2-4 mm away from the wall.
In the below picture and documentation you see how I do my mount my canvas prints.
With a little routine it is easily done in 20 seconds per corner, so time is no reason for not cutting.
Feel free to try it out yourself. I found this way to lead to the flattest backs yet providing the most stability.