How do I remove this rear plate bracket it is badly rusted

 

looking at that pic it looks as if those are rivets so would probably need drilling out and then you may be able to rub down and paint the bracket with a suitable rust proof black paint, then replace with new rivets or self tapping screws , in the UK we have smooth Hammerite for this type of work.
Interesting that my rear plate screw directly to the actual plastic bumper so I do not have that metal bracket on mine .

 

My 2011 does not have that mounting bracket either. Pretty sure it would be illegal here in Florida too. Looks like it would cover the lower part of the plate once mounted.

Curious if it is an aftermarket piece or factory.

 

My 2014 does not have it either?
Plate just screws into the plastic.
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I believe that is an aftermarket accessory because it's in the way of the viewing area of the backup camera. Do you see the top portion of the bracket on the monitor while backing up?

 

I bet the four rivets are exactly where the four holes are located on your North American license plate. My tag mounting is as previous posters noted. The tag mounts from the factory accept metric machine screws; I forget the diameter and thread pitch. Probably a PO stripped the OE inserts by inserting an SAE or sheet metal screw; this was the work-around. Once you remove this aftermarket bracket by drilling out the rivets, you should find the original inserts ruined. I would try this mounting method, since you can't access the bumper from behind:




By the way, I found this frame in a local auto parts store. It dresses up the tag, protects against car wash brushes, and is legal everywhere, as it doesn't obscure any info.

 

I don't see the bracket at all in the camera its not aftermarket its from the manufacture all the Canadian XJs have this same plate bracket

 

Use the steps member ROVIW suggests above.
But now I'm curious...
Is the center-to-center distance of the black hex screws 178 mm? That's the mounting hole spacing for North and Central American tags. Maybe you're supposed to place the tag in the bracket's pocket and attach with the two hex screws at the top only.
Perhaps your silver rivets are spaced at 232 mm, which is a common EU tag mounting dimension. Why Castle Bromwich gave Canada the Euro rear bumper cover instead of the USA is puzzling.