There is technically no size limit in Canada, although there may be bylaws that limit size, I haven't heard of any.
One handed openers are totally fine. Automatics, gravity knives, and knives that can be flicked open with one hand are technically considered prohibited weapons and are classes the same as an unregistered machine gun... So, all autos and balisongs are illegal. Assisted open knives are legal, although most police officers might not know the difference and you may have some explaining. I wouldn't worry too much about being able to flick open a knife with one hand, either. While technically that makes any knife a prohobited weapon, I've had most of my folders come through Canadian customs with really loose pivots and could be easily flicked open, even some that had been opened up and looked at, and none were confiscated. All of the knives you can buy at most of our department stores can be flicked open easily, and thousands of Canadians have been carrying them for years with no trouble with the law, so don't worry about it. Just tighten it up so the blade doesn't fly out really fast, and you should be fine.
Locking knives are totally fine.
Concealment only becomes an issue if it's a weapon in Canada. Because a switchblade, for example, is always considered a prohibited weapon because it opens with the push of a button, if you're caught with one in your pocket, you'll instantly be stuck with charges of carrying a concealed weapon whether you like it or not. Whether any other knife is considered a weapon is dependent on intent. So as long as you're not getting into trouble or using it in a threatening way towards other people, it's just a tool, and there are no laws against concealing a tool in Canada. A folder clipped to your pocket really isn't concealed anyway, so that should be fine. If anyone asks what a knife is for, never say self defence. While it would be legal to use in self defence under the right circumstances, if you have a knife in your pocket and say to a police officer that it's for self defence, that makes the knife a weapon, and the officer will most likely confiscate it and charge you with carrying a concealed weapon. If you say it's for utility purposes, and it's not a switchblade, balisong, or gravity knife, you're in the clear.
Fixed blades are also an option if you carry them. They're subject to less laws than folders for the most part. The only fixed blade knife considered to be a prohibited weapon is a push dagger. A small fixed blade knife on your belt shouldn't draw too much attention.
