I have not removed any vinyl patches bonded to R-84 canoes but have removed probably a hundred or so from Royalex canoes. Try warming the patch with a hair dryer or heat gun. Be careful not to overheat the patch as it can transmit enough heat to the hull material to crimple up the foam core, so keep checking how hot the patch is getting by touch.
Once the patch is good and warm, use a thin-bladed putty knife or paint scraper to lift up whatever edge of the patch seems loosest. Once you get one edge to start to come up, grab it with a pliers and gently lift as you continue to warm the remainder of the patch.
I have been able to reuse most of the vinyl patches I have removed in this way. Some very thin vinyl patches may become too deformed to reuse. If you plan to reuse the patch, I would clean the back of it up with acetone. Acetone can also be used sparingly to clean the hull where the patch was. Be careful, as any prolonged exposure to acetone can melt ABS, but with brief application with an acetone rag, the solvent flashes off so quickly it does no damage.
Sometimes grit and sand will work its way beneath a vinyl patch and get into the adhesive remaining on the hull after removal of the patch. In this case, you may need to wet sand the hull with fine paper (like 180-220 grit) to clean it up. There usually will be some persistent discoloration of the hull where the patch was no matter what you do.