If Laurier is leader for Canada, I wonder if there will be an immigration/emigration mechanic? That was what he was most known for from the history classes I remember.
Exceedingly boring choice if they did go with Laurier. His only real claim to fame was being a sensible leader who made good decisions and governed with above average competence.
Macdonald was a drunk who built a railroad, so a great tie in with a railroad mechanism.
Pearson was a diplomacy wonk instrumental in the creation of the U.N. and pretty much came up with the idea of U.N. peacemakers to defuse global hotspots. Natural tie in to a world congress mechanism and emergencies.
MacKenzie King was a nut job who communed with his dead mother. His dead mother was a great political advisor, as he governed longer and won more elections than any other Prime Minister. Maybe he gets a fortune telling ability that ties in with a climate change mechanism.
My personal choice, though, would be Champlain, emphasizing the age of exploration and giving Canada a chance to expand quickly and end up with a large, spread out civilization. Maybe a loyalty bonus for being far away from other Canadian cities instead of being close together.
If Canada is in there should be only one option for the UU...
Courier de bois, I hope, a unique Scout with faster movement along rivers, who adds a Trading Post in every city he uncovers.
Mountie Fort would be a good unique improvement, replacing the regular fort, giving loyaty bonus and gold bonus for trade in nearby cities.