H&B shows quite a few saddlebags mounted on a MP3 on their site. The mounting system that they offer for the MP3s are the C-Bow mounts. On the C-Bow MP3 product page, they picture the bags on an MP3, so you can get an idea of relative size and how they will look on the bike. Lots of options within the C-Bow line, plus they also offer the bag mounting hardware separately so that you can attach the hardware to any bag, and make it a removable C-Bow bag.
The pricing on H&B across the line is quite pricey, however for quick-release removable saddlebags, I believe they are the only option on an MP3 (besides fabbing up something of your own) plus when running without the bags, the mount is fairly minimal compared to most structures for removable saddlebag mounts.
Ultimately my favorite choice would be the Xcore hard bags in natural aluminum, however the US distributor, MotoMachines is the exclusive distributor to order them here, and they cost $738 for a pair of bags, plus another $70 (each!, so $140 for both) if you want the soft inner bags fitted for them, plus then the mount, $306 for either the 350/500 or the 530 mount. So that's $1044 for the mounts and saddlebags, or $1184 with the soft inner bags too. Ouch!
I ordered the mounts before the price increased due to tariffs, but I'm still waiting for them, as they are coming from Germany. MotoMachines told me they only ever offer discounts on Black Friday & Christmas week, but they offered me a 5% first order discount (Coupon Code "Welcome5"), so I was able to get the mounts for $264. I ordered them as I also found a pair of barely used H&B Royster Speed C-Bowbags on eBay for $140, that list for $414 on MotoMachines, plus it included a couple generic rain covers. H&B charges about $80 (each! $160/pair) for rain covers, which is basically a somewhat fitted shower cap. The Royster bags are somewhere between a soft and hard bag, so will likely offer some protection to the bike, plus they are unlikely to break in a tip-over event. Not my first choice, but quite content with saving so much over my first choice. For the eBay price, it was less than buying the bag hardware only, which I could always take off the Royster bags and fit them to any other bag from any manufacturer if I wanted as well.
If there isn't an exclusive Canadian distributor for H&B, you can order directly from H&B, & they have a 50th anniversary sale coming up May 30-31 & June 20-21. It's just available in their outlet, & won't be listed on their site, so you will have to call or email them during this time to see what's available. They can't ship to me as MotoMachines is their exclusive distributor in the US.
To see a couple bags on your 500:
https://www.hepco-becker.de/en/c-bow-sidecarrier-for-piaggio-mp3-500-2015.html
To see a half-dozen bags on the 530, which still should help you decide:
https://www.hepco-becker.de/en/C-Bow-sidecarrier-black-for-Piaggio-MP3-Exclusive-530-2022/6307650-00-01
Lots of other compatible C-bow bags available other than these however.
I like a hard case, and the X-core aluminum would be visible to drivers, plus match the aluminum on my bike. The 530 link shows a black X-Core case on the bike, and it looks appropriately sized. The Roysters are quite nice though and reflective, so I'm happy with what I have, and will probably only upgrade if I damage them, or find a deal on the X-cores, or another style I like that I can move my Royster hardware to.
I wondered why so many get top cases vs side cases as the weight is down low and further forward for better handling & aerodynamics, plus I think they look better too. However I now know, as the prices for a top case are far less for more storage combined with a pillion backrest. I got a Shad SH59X, adjustable hard top case (expandable between 46, 52 and 58 liters, MP3 specific quick-release lockable mount, inner bag, & pillion backrest all for $379, all-in shipped from Italy. (I usually don't like the look of a top case, but this one is wide, so when viewed from the side it's not that large when in the 46L position, yet wide from the back which I like for more visibility.) So $379 for 58L of storage with the bonus of a backrest, vs $1184 for a combined storage of 36L (18L each) on the Xcore bags. So for sidebags, it's more than a third less storage for three times the price, without the added benefit of a pillion backrest.
The Roysters I bought are 13L each or 26L, so I'll have a total maximum added luggage space of 84L, which should give me a lot of added utility for the $793 spent. Between the storage and a bit of added protection for pillion, rider and bike, I'm happy with the outcome, especially because they are all quickly removable.