I too have seen gloss differential (GD) and bronzing with some photo papers using the Canon Pro 4000. Canon's satin photographic (240 gsm) and Canson's satin photo papers showed the least amount of GD and bronzing of any photo paper I have tried to date. Epson's premium luster, legacy baryta, and Canson's baryta were the worst for GD and bronzing -- even with chroma optimizers set to overall. With this said, you really have to look for the GD and bronzing to see it. Viewed at a normal angle with appropriate lighting, all of these prints are exceptional.
Using same OEM inkset on Pro-1000, CO overall, I have some of the worst results in this regard on Hahnemühle Photo Silk Baryta, making it a pain for table pass-around reviews.
But today I tried (among many other papers recently for finding a match to this new printer/inkjet) the newer Canson Prestige, and although I prefer the texture (both front and back) of the cotton Platine over the more uniform, almost Canson RC Luster-like, surface of the Prestige, gloss differential and bronzing almost went away, to my big surprise, as no other tested paper yet has even come close. The Platine is better than the HM Silk Baryta, but the Prestige seems to be in a different league, hopefully making this a non-issue. It is an issue with many other papers I feel, possible not when glazed and walled, but when passing prints around a table for review/client discussions, it can really look nasty with overhead lights and people noticing the odd look.
I here good things about some new Canon FA series, but haven't had a chance to try it out yet. But seeing this today, I have hope that other well behaved papers for this printer might exist.
Now the question begs if this apparently different technology of the Prestige has already found itself into other papers I haven't tried yet, or when this new tech will find itself into new versions of something like the existing Canson Platine with all it's otherwise wonderful qualities (in my eyes and hands). Anyone with sufficient insight here to give an informed tip or forecast?