I must say, adding Canada would be really strange, since it is so young
I agree, I would never want to see Canada in any Civ game. The only time I would accept Canada in any Civ game is if there were a senario that allowed for them. World Wars 1 and 2, Korean War, war of 1812(Technically pre-Canada but still part of our/MY country's history)
As for other nations and leaders.
Definitely:
Celts(Includes both Scotish and Irish)
Norse(Vikings)
Babylonia(You just can't do without)
Ottomans(Would certainly Make nice addition)
Zulu
Vietnam
Possibily:
Sioux
Huronion
Iroquois
Mayan
Now I will admit that there are more that need to be added to BOTH of these lists. This is simply my condensed version.
The possibly list is simply because I believe that those nations should have some home in Civ. Each of those nations played an important role in forming North America. Especially the Huron and the Iroquois durring the hundred years war until the Huron nearly died off completely due to plagues and pox.
As for leaders I was sorry when I saw selection for some nations. They left out some extremely important leaders for many nations.
Russia: Stalin
England: Richard the 3rd(Richard the Lionheart), Winston Churchill
France: Joan of Arc(She Led armies and deserves to be here as much as many others)
United States: Eisenhower, Lincoln, Ulysses S. Grant, maybe even Kennedy
Rome: Constantine, Augustus
And again there are many more still. But Those are again the ones that I know should have been there, and were left out.
The are some ways that more civs can be introduced, that is to provide senarios where those civs took part. Example, North America Pre-European and just a little after thier arrival say until 1750. That gives an opportunity to have many native american tribes with out having actual civs.
I happen to be someone who likes playing senarios rather than other people, dunno why I'm just that way. And so as far as senarios go:
*Americas Pre-European(Explained a little above)
*100 Years war(It war probably first TRUE world war in that there was fighting on EVERY continent)
- The specific location is not as important as the stroy behind it
(Being from Canada I am really only aware of 100 years war with relation to french Canada)
*World War 1 & 2
- This gives great flexibility, can be fought in Europe, (Already African Campaign), Japan/Pacific, South East Asia, Russia(Near and around Stalingrad)
- Roman Expansion (It's been done but why not go with a good thing)
I think that is everything that I thought up in terms of additions. It is far from having ALL nations that deserve to be in the game but these are all of them the I want to see in the game. (Wouldn't mind seeing more though)