Quarantine tank and treatment

Hello everyone
I am getting back into the hobby after a break.
My plan is to order some fish from different sources and putting them through quarantine first before they go together in one tank.

My question is what kind of meds do you guys put into the quarantine tank to tread them for all kinds, as a precaution. (Internal and external diseases)
Since Canada has banned many aquaristic medications, what do you use and where can I get it?

Thank you for your help

I use no meds. Fish meds are kind of crude, and are only for use if you can identify the exact problem you are going after.
If you have bought standard pet store fish, your problem can be the fish coming off of meds. The cheaper farms often use antibiotics fairly indiscriminately, which doesn't help the fish with immunity or gut flora. Some even use hormones for colour - another whole issue.
A QT tank has to be spacious, clean, cycled and set up to minimize stress. Improv QTs can be deadly.
There are meds I keep on hand, to be ready, but in Canada, we are really limited. I always have malachite green or malachite green concoctions with formalin, or methelyne blue, in case of Ich or velvet.
I wish I could easily have praziquantel, for run of the mill tapeworms, and levamisole or flubendazole for Camallanus nematodes is great to have. Most puppy forms are not water soluble so you have to make paste foods - but Camallanus are still not super common.
You need a book or well visited site with common fish diseases illustrated. so you can study what they look like and avoid them.

Things like melafix are not very good. They are extremely weak, as if their active ingredients were present in the quantities need to kill bacteria, they'd kill fish too. Some of the remedies out there are pretty close to homeopathic.

I'm in Quebec, and aquarium antibiotics were banned here long before the rest of Canada. I've learned, quite frankly, that they aren't missed. You need to know exactly what the problem is before you ever use antibiotics, and I don't have a lab in my house. Shotgunning valuable medications at poorly defined problems is trying for luck and wasting resources. With clean water, careful buying (if you have even a twinge of doubt, don't buy that fish! Trust your instincts) and well set up QT, I lose fewer fish than when I used to trust meds to fix my mistakes.

Excellent advice @GaryE

Now I know how the fish feel.

We have all been self-isolating for a while.
When do we get to go into the big tank ??

Ich has never been a pandemic in my tanks.
However I have seen many hobbyists catch the tank bug.

I was trying to flatten the curve with my guppies.
Funny, even though I stayed 2 meters away they still kept growing.

@GaryE has hit the nail on the head.  The preponderance of aquarists who love to dose with some mysterious cocktail of unknown meds "just in case", as a preventative, is frightening.  Behaviour like that is what led to the move by the government to ban meds, thanks to the rise of antibiotic-resistant strains of bacteria that were once easily controlled...but no longer.  

In typical fashion, Big Brother responded in an overly-draconian knee-jerk fashion, but by and large I aoplaud the sentiment.  Anyone else who has ever had an elderly relative in a hospital or care facility that was in partial lockdown mode thanks to antibiotic-resistant bugs understands what I mean.

So, in answer to your questions:

What do you use? Water. Clean, unpolluted water.

Where do you get it? Usually, out of your tap. Pre-treat (not medicate!) to remove chlorine and/or chloramine...temperature match...and in most cases you are golden.

Utilize your common sense when buying and selecting fish. Don't buy them if they look sketchy, don't buy them if they were kept in unhealthy-looking conditions; doesn't matter how much you want them if they are already pre-disposed to fail. Prevention always trumps seeking a cure.

@GaryE thank you very much for your informative reply and advice.