YES, you can stretch injet canvas! We do it all the time.
We have to allow at least 24 hours (48 is better) drying time for the printed canvases. We print on PremierArt Water resistant Canvas. We stretch the dried prints on wooden stretcher strips and staple, pretty much like you would a regular canvas painting. You begin with one side and staple in the center of the side (or on the back if you have enough canvas to pull to the back and don't want to see staples on the side edges - either is acceptable). Then, you switch to the opposite side, pull tight (with fingers or you can use canvas stretching pliers) and put a staple in the middle. Then do the other two sides. Once you have all four sides with at least one staple, you can begin pulling the canvas tight on the first side you started with, and stapling down the edge, leaving some space at the corners (you will do corners later). Repeat with the opposite side and then move onto the third and fourth sides.
Now you have to make nice corners. This gets tricky but what you are basically doing is wrapping a package. You want your corners to be neat and not too bulky.
Here is a site that illustrates canvas stretching:
http://www2.evansville.edu/studiocha.../p-canvas.html
After the canvas is stretched, we typically use a product called Tight'N Up canvas retensioner, sprayed on the back, to ensure the canvas is tight (but not overtight). We also seal the image after stretching with a product called PremierArt Print Shield Laquer.
I hope this helps.
Tracy