I just got back from using the Shiloh before I put her away for the winter. Getting to cold for me, and its hard to use gloves on the set trigger.
There isnt alot in common with the light bullets used in lever guns and the big single shot numbers that start at 500 grains. The stock shape, weight, drop, everything is different. Same with the round ball muzzle loaders there is no comparison whatsoever, a 54 cal with a minie ball is pretty mild in comparison. You really need to consider where your brass is going to come from, I beleive Shooters Choice will carry some as will Bullet barn, and there are gun shows ext.... But you are looking at a substantial outlay in cash for a few hundred peices of brass. Money that can be spent on better quality sights or a fancier gun. Your probably going to want at least 200 peices of brass for the gun, probably more. Your going to be experimenting with a few mould sizes, and they dont come cheap.
Now to adresse a few things in your post that show some warning signs
I would like to know if there is any place in Canada where I can purchase brass
What gear do I need to buy besides a lead furnace and bullet molds?
Pretty clear this is your first "big" single shot, and because of that you really, REALLY, should consider getting one in 45-70 because thats the most most men can shoot prone without a sissy pad. Your brass is cheap, there is well established and succesful load combinations worked out and available for nearly any one of the target bullet shapes and with a Shiloh you can load your shells with smokeless and get very close to any of the bigger black powder shells velocity wise. Getting smokeless to work in the bigger cases is possible, but its way easier with black. With the 45-70 its pretty simple to get very satisfactory accuracy with various different types of powder on a plain base bullet. Go ask the same thing on the Shiloh forum and they will tell you get the 45-70. Theres moulds made with reduced diameter driving bands that allow you to seat your bullets way out of the case for extra capacity and you can also paper patch.
The 45-100 recoil is not that bad, but its noticeable, a 45-90 with an actual heavyweightl target bullet is nearly identical, and the 45-90 brass seems to be easier to come across. If you must have a bigger shell, consider a 45-90 or shiloh calls it the 45-2.4 again theres lots of guys who have come up with excellent recipes for this shell, its very popular with the guys who shoot longer range. I agree with MoonCoon in you should try one out if you can, because shooting prone from cross sticks will feel much MUCH different then offhand shots with these guns. Have you shoot you're 300 or 340 Weatherby prone for a string of 20-50 shots? Probably not, but you likely will with the Sharps.
For gear, you start with the gun and work your way up. Buying cheap gear will bite you in the rear end later. For good sights your looking at 500 bucks easy for a good set and it goes up, way up from there. You need a subtantial one peice cleaning rod if your shooting black, something like the biggest Dewey or Tipton rod you can get ahold of. Wad punches if your loading for black powder, wad material (youl probably want to try underprimer, under powder and overpowder wads and theres more types out there). You need come way to compress the powder, eather a compression die, a drop tube, or if your a skinflint like me just use an RCBS 45-70 expanding die. You need some way to lube the bullets if you shoot grease groove, Im lazy so I use bullet lubesizer, but you can pan lube if you want. You need the lube itself, again Im cheap I use toilet bowl wax mixed with ATF for smokeless and Lard mixed with beeswax and vaseline for black powder. You'l need lead....................lots of it. If your shooting black powder your going to need a blow tube or lots and lots of patches.
These guns require a
QUALITY bullet which can only come from a
QUALITY mould, Lee does not make moulds suitable for this application in my opinion. The moulds get pricey once you start experimenting with different shapes, alloys and combinations. If you've never cast bullets before, you picked the hardest type of gun to learn to cast for.
Your about to go on a pretty big adventure in shooting and reloading, it should be enjoyable. Lots of guys buy guns for the larger shells and give up, get discouraged and sell the thing before they get the chance to get some accurate shooting out of it and thats the biggest shame of all. With a smaller shell you will get satisfactory results way quicker and not have a discouraging learning curve.
Besides if you still want the 45-100 you can always send it back to Shiloh and get it reamed out to the bigger case later, it doesn't cost much.