There are two routes I'm aware of you could take.
First, you could weld the hole shut. You'd need to clean the area of rust/corrosion with a sander, then get a small circular punch out of the same size (diameter/thickness) of metal as the hole, hold it in place, tack weld it, then finish weld it, then paint match it to keep rust at bay. (General description of the process.)
If aesthetics are not an issue (going to be covered by carpet, never to be seen) and/or you don't have access to a welder, you could try using fiberglass sheeting and rust converter.
I bought my son a Jeep Cherokee where the floor at the driver's seat was riddled with rust holes. Nothing big (mostly pinholes) and nothing structural. I cleaned up the area the best I could, then took some fiberglass sheeting and cut some to size. I applied some POR-15 (this is what I used ... any rust converter should do the same job) to the metal, then stuck the fiberglass to it, then painted over the fiberglass. I did this from the bottom side. Once dried, the coating provided an air/water tight seal. It also becomes as hard as a rock. You can do this to both sides if you like, but the bottom side is sufficient for it to work. If you do go this route, be aware the POR-15 will stick to everything and won't want to come off. Any paint brush you use will be ruined. It will also bond two pieces of metal together, so once you've gotten it on the sides of the can as you are trying to dish it out, the lid will bond to the body of the can, which means you'll never get it open again. The stuff coats very well, so even a small can would be enough to do just the single hole you're showing in the picture, or even many small holes (if that's what you've got going).