There has never been a prime ministerial dynasty in Canada.
John A. Macdonald’s son, Hugh John Macdonald, became federal cabinet minister and the eighth premier of Manitoba, but never prime minister of Canada.
[N.B. Daughters don’t count!]
Wilfred Laurier did not have a legitimate son.
Nor did Robert Borden.
Nor did R.B. Bennett.
Nor did William Lyon Mackenzie King.
Nor did Louis St. Laurent.
Nor did John Diefenbaker.
Lester Pearson did have a son, but Geoffrey Pearson became ambassador and never ran for office.
Jean Chrétien’s son, Michel (born 1968), does not appear to have any political ambitions. He was adopted as a Gwichʼin child from an Inuit orphanage.
If Paul Martin senior had become prime minister, as he wanted to be, the Martins would have become the first Canadian prime ministerial dynasty the moment Paul Martin junior became prime minister.
Justin Trudeau may – or may not – make history.

And if not Justin this time round, perhaps in a few years Sarah Coyne, Pierre’s only daughter:
http://www.yourhome.ca/homes/news/world/article/895866–pierre-trudeau-s-daughter-sarah-lives-under-the-radar
Woops. Just remembered “daughters don’t count!” Sorry Sarah.
How many does it take to be called a dynasty? Does the “dy” prefix imply two?
-15c. (earlier dynastia, late 14c.), from M.Fr. dynastie and directly from L.L. dynastia, from Gk. dynasteia “power, lordship, sovereignty,” from dynastes “ruler, chief,” from dynasthai “have power.”
That’s what my Chambers Dictionary of Etymology says too but doesn’t that suggest that one ruler excercising power constitutes a dynasty?
Yes, it certainly does, It suggests every ruler is a dynast even if he has no dynasty.
I just hope that we are discussing merit here as well.
Kiss the Liberal party good-bye if Justin becomes leader.
St. Laurent had no sons? That may be a surprise to his sons Renault and Jean-Paul, especially since the latter was an MP.
How embarrassing for me. I apologize. I only know of a daughter. Google did not mention any sons – or they eluded me somehow.