Knowing that your final output is canvas, you will need to allow for the edges. With large canvas prints you'll need 1-1 1/2" inches on each side for the edges. That means your final image will need to be 27x39 inches leaving 1 1/2 inches on each side.
Edges can be mirrored or wrapped depending on your preference and the type of canvas mounting. I found mirrored images work well.
I know this is being picky about detail, but in larger prints the defects are increased in size to the point where they are easily noticed. You have enough detail in the file for a good print if you handle it correctly. If you are making a large canvas print, you want it to be first rate work and you really don't want to re-do it.