What I find funny about the discussion of our Constitution and slavery by a Canadian is that when it was written, 1787, slavery, as abhorrent as we find it today, was standard operating procedure around the world in that time period. He11, even the UK did not abolish slavery until 1833, which was some years after our Constitution was written and enacted.
On top of that, the part in the Constitution which counts slaves as 3/5 for representation purposes was not the current narrative: Racism in thinking blacks were worth less than whites. In fact, it was quite the opposite. Those Founders who were sickened by slavery saw it as a dying institution, though not dying fast enough by any means, and they could not stop it at that time due to a number of factors, including money and war weariness. So the 3/5 number was designed to be antislavery, which is counterintuitive. By limiting the weight of representation of the Southern states, the Founders were limiting the slaveholding states' impact on national policy. If slaves were counted at 100%, then the south could have been able to maintain a national policy of slavery far beyond their slaveholding numbers. In the end, slavery would have lasted far longer than when it ended in 1864-1865.
But I do find it humorous that someone from Canada is criticising our Constitution over the slavery issue when the UK still had slavery as well, and that included Canada.