First, I didn't know Canada had founding fathers. Interesting.
But just in case we're talking about the US founders, it is pretty misleading to say they founded a slave-owning republic (I'm sure you didn't mean "owing" ... or maybe you did?). The whole 3/5ths of a person dust-up is proof they were deeply divided on the issue from the getgo. They all had a major common enemy in Britain (at the time - of course all is well now). But the northern colonies were generally against slavery and the southern colonies were not.
Now the south was making trouble by trying to get their slaves counted as full persons for representative purposes (to enhance the south's congressional presence) but as non-persons for tax purposes (to lower the tax base). The north stuck it to them and said basically you can't have it both ways. Thus the 3/5ths deal was struck as a temporary compromise during a time of extreme duress.
So the founders didn't view the republic as sanctioning slavery. They simply let slave-owning states join up with the free states to fight the more immediate problem of British oppression, but with a clear intent to not let the south rest easy with its slavery either. One problem at a time. It?s a mistake to lump these guys all together into some weirdly uniform modern stereotype. They were a complex and rather advanced collection of thinkers, well ahead of their time in many respects, planting at the outset the seeds of slavery's demise.
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