I like to finish the back on my paintings. However, I have learned not to finish the back until the piece is sold. There have also been trial and errors, cutting with scissors or a blade always seemed off. So I did some research and discovered a blade made specifically for the task (and of course framers already knew this). Here is my video on adding a paper backing to your painting.
Step 1: Make sure you lay the painted side on something soft.
Step 2: Attach double sided extra strength tape.
Step 3. Cut the paper slightly large than your painting and attach to the back of the canvas.
Step 4: Crease the edges of the paper.
Step 5: Place the dust cutter trimmer against the edge and slowly cut the edge of the paper. The trimmer will leave a clean ¼ inch straight cut!
Step 6: Spray water all over the back of the cover and allow to dry, the water will tighten the paper as it dries.
And wella the painting now has that finished backed look!